Heat olive oil in a large skillet over medium heat. Add lion’s mane mushrooms to the skillet and cook until they begin to brown and crisp on the edges, stirring, pressing with a spatula and flipping occasionally. This usually takes about 8-10 minutes. Remove the mushrooms from the skillet and set them aside.
In the same skillet, add more olive oil if needed, and stir in sliced red, green, and yellow or orange bell peppers, along with sliced red onion or shallots. Cook until the vegetables start to soften and get a bit of color, about 5 minutes.
Slice the cooked mushrooms into bite-size pieces and add it to the skillet along with the minced garlic, and then sauté for a few minutes just until the garlic is fragrant.
Sprinkle Mexican chili powder, black pepper, sugar, ground coriander, ground cumin, stock or water, chipotle peppers in adobo sauce (if using), and salt over the mushroom and vegetable mixture. Stir well to combine and cook for another 2 to 3 minutes.
Warm tortillas for a few seconds on each side directly over an open flame, or by placing them in a dry skillet over medium heat for about 25-30 seconds on each side until they are soft and pliable.
Assemble the fajitas by placing shredded lettuce and spooning the lion’s mane mushroom and vegetable mixture onto the center of each tortilla. Top with a dollop of vegan sour cream, sliced jalapeños, finely minced red onion, and cilantro leaves.