Ripe red tomatoes work best for their sweetness and low moisture, but firm green tomatoes can be used if you prefer a tarter bite—just increase baking time by a few minutes.

Yes, all ingredients are naturally gluten-free, but always check your mustard labels to be safe.

Can I prepare these ahead of time?

You can assemble the tomato slices with the topping up to a few hours in advance and refrigerate, then bake just before serving. Avoid baking ahead as they get soggy.

Keto Baked Parmesan Tomatoes Recipe – Easy Low-Carb Side Dish

Name: Parmesan Tomatoes
Prep time: 15 min
Cook time: 15 min
Total time: 30 min
Yield: 4
Cuisine: Keto
Ingredients: ripe tomatoes, sliced; tablespoons mayonnaise; tablespoons Parmesan cheese; tablespoon Dijon mustard; tablespoon brown mustard; teaspoon dried oregano; salt and pepper to taste; teaspoon chopped fresh parsley; /4 cup shredded mozzarella cheese

Ingredients

ripe tomatoes, sliced
tablespoons mayonnaise
tablespoons Parmesan cheese
tablespoon Dijon mustard
tablespoon brown mustard
teaspoon dried oregano
salt and pepper to taste
teaspoon chopped fresh parsley
/4 cup shredded mozzarella cheese

Instructions

Step 1

First, I preheat the oven to 350°F (175°C) and line a baking sheet with parchment for easy cleanup. While the oven heats, I slice four ripe tomatoes into thick rounds, about half an inch each, and arrange them in a single layer. In a small bowl, I mix together the mayonnaise, both mustards, Parmesan, oregano, salt, and pepper until smooth. Then I spoon a generous dollop onto each tomato slice, spreading it just to the edges. A sprinkle of shredded mozzarella on top adds that irresistible stretchy cheese pull, and a final dusting of fresh parsley brings a pop of color. Into the oven they go for about 15 minutes, until the tops are bubbly and golden. I watch closely near the end to avoid burning. Once out, let them rest for a minute before serving—they’re piping hot. These are best enjoyed right away, straight from the baking sheet.

Chef's Tip

I always use full-fat mayonnaise and freshly grated Parmesan here—the pre-shredded kind doesn’t melt as smoothly. Also, patting the tomato slices dry with a paper towel helps the topping cling better and prevents a watery bake.

Storage Tips

Leftovers keep in the fridge for up to 3 days, but they lose some crispness. I reheat them in a hot oven or air fryer for 5 minutes to restore the golden top.

Variation Tips

Swap the mozzarella for sharp cheddar to give the dish a bolder flavor, or add a pinch of red pepper flakes for heat. Try using different mustards like whole-grain or spicy brown to change up the tang. These tomatoes pair beautifully with grilled chicken or a simple arugula salad.

Parmesan Tomatoes