Move over white bread tuna melts! One taste of these low carb ones and you’ll never look back!
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I love a good tuna melt. And I can honestly say that these keto tuna melts on a portobello mushroom base have got the regular bread version beat, hands down.
Plus, they have a surprise ingredient!
This is a tuna melt without bread!
Now don’t get me wrong. I love bread and a good sourdough tuna melt is pretty great as well.
But that being said, any time I can get in extra veggies and love the finished result even better, I say that’s a win!
The mushroom base is the perfect complement to tuna! And it also keeps keeps the melts low carb for a Trim Healthy Mama S meal.
How to prepare the mushrooms
To get the mushrooms ready to bake, I first gently scrape out all the gills.
I pre-bake them on a rack to get them soft and let the mushrooms release a lot of liquid. Then I can pat them dry before adding the toppings. This way I don’t end up with soggy mushrooms!

What is the surprise ingredient?
You’ll never guess, so I’ll just tell you! The bottom layer on these tuna melts are shredded turnips that have been sauteed just until tender.
This may sound like a strange addition but trust me on this. I would never steer you wrong lol.
The turnips are what take this recipe from ‘good’ to ‘WOW’!! They get slightly sweet from being sauteed, yet are still earthy. Pair that with a hearty mushroom base, mouth watering tuna filling, and the fresh pop of tomato on top and this meal is a winner!
Plus, even more veggies!
I especially love sprinkling some fresh basil as a finishing touch. But unfortunately it is not growing season for me at the time of writing this. And my small town where I get groceries does not have something as exciting as fresh basil, lol.
So alas, no basil in these photos. But it adds extra freshness and delicious flavor.

These keto tuna melts have cheese but are still a light meal
Sometimes we associate cheese with THM Heavy S casseroles and dishes and perhaps shy away from it. With good reason. Overdoing cheese can definitely stall weight loss.
But assuming you aren’t sensitive to dairy, these tuna melts shouldn’t be a problem. There is just a small amount of cheese on top.
The water content of the mushrooms, plus the addition of turnips adds plenty of nutrition and lightness to this recipe.
You won’t feel heavy or weighed down after eating, but light and nourished. I like to serve them with a side salad for a super veggie packed and weight loss friendly meal.
Why eat fish?
There are many great reasons why we should be including more fish in our diets. Here are a few of them:
- Fish contains healthy Omega 3 fats
- Supports a healthy heart and brain
- Is a light and lean source or protein
- Is quick cooking and canned tuna or salmon is great to have on hand for easy meals.
In fact, Trim Healthy Mama did a whole podcast episode just on why you should be eating more fish! You can listen to that here: The One Food You Need To Eat Way More Of.

Is tuna safe to eat?
You sometimes hear concerns about tuna and the mercury levels in it. But there’s no reason to never eat it again.
While tuna might contain trace amounts of mercury, not all tuna types are created equal.
The two main kinds of canned tuna are chunk light and chunk white or solid. According to this article, chunk white, which is albacore tuna, contains up to three times the amount of mercury as the skipjack, or chunk light tuna.
An adult can safely eat chunk light tuna once a week.
Keto Portobello Tuna Melts Recipe:
Ingredients:
4 large portobello mushrooms
1 cup tightly packed shredded turnips
2 cans chunk light tuna, drained
2 tablespoons sugar free relish
1/4 cup mayonnaise
Salt & pepper to taste
Sliced tomatoes
Sliced cheese of choice
Fresh basil to garnish, optional
Ingredients:
1. Gently scrape the gills out of the mushrooms and place on a cookie cooling rack on a baking sheet. Bake at 425 degrees Fahrenheit for 20-22 minutes or until softened.
2. While the mushrooms are baking, saute the shredded turnips in olive oil until tender and season to taste with salt and pepper. Mix together the tuna, relish, and mayonnaise and season to taste with salt and pepper.
3. When the mushrooms are done cooking, drain off any liquids and pat completely dry with paper towel. Divide the sauteed turnips evenly between them and then top with tuna salad. Place a sliced tomato on top and finish with a slice of cheese.
4. Return to the oven and bake another 10 minutes or until heated through and the cheese is melted. Top with fresh basil if desired.
Print this recipe here:
Portobello Tuna Melts
Ingredients
- 4 large portobello mushrooms
- 1 cup tightly packed shredded turnips
- 2 cans chunk light tuna drained
- 2 tablespoons sugar free relish
- 1/4 cup mayonnaise
- Salt & pepper to taste
- Sliced tomatoes
- Sliced cheese of choice
- Fresh basil to garnish optional
Instructions
- Gently scrape the gills out of the mushrooms and place on a cookie cooling rack on a baking sheet. Bake at 425 degrees Fahrenheit for 20-22 minutes or until softened.
- While the mushrooms are baking, saute the shredded turnips in olive oil until tender and season to taste with salt and pepper. Mix together the tuna, relish, and mayonnaise and season to taste with salt and pepper.
- When the mushrooms are done cooking, drain off any liquids and pat completely dry with paper towel. Divide the sauteed turnips evenly between them and then top with tuna salad. Place a sliced tomato on top and finish with a slice of cheese.
- Return to the oven and bake another 10 minutes or until heated through and the cheese is melted. Top with fresh basil if desired.
You might also enjoy these recipes:
Cream Cheese Stuffed Mushrooms with Lemon and Herbs
Southwestern Chicken & Rice Stuffed Mushrooms
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