Prepare the ingredients: Slice the mushrooms into ¼-inch thick slices. Thinly slice the onion and mince the garlic.
Cook the onions and garlic: Heat olive oil in a large pan over medium heat. Add the onion and garlic, and sauté for 2-3 minutes until softened and aromatic.
Sauté the mushrooms: Add the sliced mushrooms to the pan. Cook, stirring occasionally, for about 5-7 minutes, until the mushrooms release their moisture and begin to brown.
Season the mushrooms: Sprinkle the cumin, chili powder, smoked paprika, salt, and pepper over the mushrooms. Stir well to combine and cook for an additional 1-2 minutes, allowing the spices to bloom.
Warm the tortillas: While the filling is cooking, warm the tortillas in a separate pan or in the microwave until soft and pliable.
Assemble the tacos: Once the mushroom filling is ready, spoon it into the warm tortillas. Top with sliced avocado, fresh salsa, sour cream (or its vegan alternative), and chopped cilantro.
Serve and enjoy: Serve the tacos with lime wedges on the side for an extra burst of freshness.