Heat a pan with oil, add the onions, stir, cook for a minute or until caramelized. Set aside.
In the same pan, add oil if needed, saute the garlic. Add the bell pepper, cumin, chili powder, smoked paprika, salt, and pepper, stir to mix. Add the salsa, stir, cover, simmer for a minute or until the bell pepper is tender.
Add the mushrooms, stir, cook for a minute or until tender. Add the caramelized onion, stir until well heated. Remove from the heat. Lay the lettuce leaves on a platter. Fill each leaf with the veggie fajitas, squeeze some lime and garnish with cilantro.