Combine lime juice, vegetable oil, red pepper flakes, and garlic in a plastic bag. Seal, shake well to combine. Add chicken breasts to the bag and allow to marinate for at least 1 hour and up to 8 hours.

Place chicken in a non stick skillet and sprinkle to taste with fajita seasoning. Cook on medium high heat until cooked through. Cut into small pieces and set aside.

In the same skillet, heat 1 tbsp. of olive oil on medium high heat. Add mushrooms and sauté until tender, about 3 minutes.

Add the chicken and spinach, and sauté just until the spinach is wilted, about 30 seconds. Transfer mixture to a bowl and set aside.

Brush pan with olive oil. Divide mixture among tortillas, sprinkle lightly with cheese. Cook in pan, flipping occasionally.

Cut into triangles and serve