Step 1

Preheat the oven to 375 degrees F (190 degrees C).

Step 2

Cut bell peppers in half vertically through the stem and remove the seeds. Place cut-sides down in a baking dish to allow excess moisture to drain.

Step 3

Bake in the preheated oven for 10 minutes. Remove from the oven, flip peppers over, cut-sides up, and set aside.

Step 4

Heat oil in a large skillet over medium-high heat. Cook meatless ground beef and onion in the hot pan, breaking up any large pieces, until browned, 5 to 6 minutes. Add garlic and stir until cooked through, about 2 minutes more. Sprinkle with taco seasoning and stir in diced tomatoes until combined. Stir in 3/4 cup Mexican cheese.

Step 5

Stuff peppers with mixture and cover dish with foil.

Step 6

Bake in the preheated oven until peppers are tender, 10 to 15 minutes. Remove foil and top peppers with remaining cheese. Return to the oven and bake until cheese is melted, 2 to 3 minutes. Sprinkle with cilantro and serve each pepper with a dollop of sour cream and guacamole.