Heat the oil in a large skillet on medium-high. Stir in garlic, onion, mushrooms and pepper and saute for 4-5 minutes until vegetables are soft and lightly browned.
Turn the heat down to medium and stir in the cumin, chili pepper and salt. Cook for an additional 2-4 minutes until spices are incorporated and aromatic. Mushrooms release some extra liquid so feel free to pour some out or use a slotted spoon to scoop them out of the pan.
Spoon the vegetable mixture into taco shells and garnish with cabbage. Garnish with a squeeze of fresh lime and serve warm.