To make the filling, first coat the bottom of a large skillet with the olive oil and place it over medium heat. Give the oil a minute to heat up, then add the onion. Cook the onion for about 8 minutes, stirring occasionally, until it softens and starts to brown.
Crumble the tofu into the skillet. Cook it with the onion for about 5 minutes, stirring occasionally, until it dries out and starts to crisp up in spots.
Add the garlic, cumin, and chili powder to the skillet. Stir to combine the ingredients and cook everything for 1 to 2 minutes, stirring constantly, until the mixture becomes very fragrant.
Stir in the tomato sauce, adobo sauce, soy sauce, and black beans. Bring the sauce to a simmer and let the mixture cook for about 5 minutes, stirring occasionally, until the sauce thickens up a bit.
Remove the skillet from heat and stir in the corn and cilantro. Season the filling with salt and pepper to taste. You can adjust any other seasonings to your preference at this point as well.
To assemble the burritos, arrange a quarter of the spinach leaves and avocado slices in the center of each tortilla. Divide the filling among the tortillas, placing it over the spinach and avocado slices in a short strip. Fold the side of the tortilla closest to you over the filling, tuck in the sides, then roll the burrito away from you.
Serve.