Preheat oven to 375ºF. Line a large rimmed baking sheet with parchment paper. Set aside.
Heat olive oil in a large pan over medium heat. Add the garlic and cook,stirring, for 30 seconds or until garlic is fragrant.
Add the mushrooms and onions and continue to cook, stirring occasionally,until softened, 5-8 minutes more.
Place walnuts in a food processor and pulse until powdery but not sticky.
Add the mushroom mixture and chipotle pepper with adobo and process until fully combined and still slightly chunky. If the mushrooms are still hot, open the feeding tube on the processor while processing to let steam out while you process.
Transfer the mixture to a large bowl. Add the breadcrumbs, egg, taco seasoning, salt, and pepper. Stir until the mixture is well combined.
Transfer the mixture to the prepared baking sheet and spread out in an even layer. Bake 30 minutes, stirring and breaking it up once halfway through.
Serve in tacos, burritos, or salads with lettuce, tomato, avocado, salsa, and your other favorite toppings!
To make a flax egg, combine 1 tablespoon flaxseed meal with 2.5 tablespoon cold water. Stir to combine, then let rest in the refrigerator for 5-15 minutes until thickened.
Tips for customizing
Add more or less taco seasoning and chipotles to taste
If you don’t have taco seasoning, use ½ tablespoon chili powder, 1 teaspoon cumin, and more salt to taste
Swap the walnuts for pecans, sunflower seeds, or any combination of the three
Non-vegans can substitute one egg for the flax egg