In a small bowl, whisk together 3 tablespoons of vegetable oil with the garlic, salt, chili powder, ground cumin, paprika, sugar and lime juice. Set aside.
Heat a large skillet over medium-high heat. Add the oil and then stir in the chicken. Cook for 2 minutes or until the chicken is lightly browned. Stir in the onion, bell pepper and mushrooms and cook with the chicken for 3 to 5 minutes or until the vegetables are tender.
Stir in the spice mixture and cook for another 2 minutes or until everything is well combined and heated through. Season with salt and pepper to taste. Serve with tortillas and optional toppings.