Heat 1 tablespoon olive oil in a large skillet over medium-high heat. Add in onion, bell pepper, and mushrooms. Saute until vegetables are tender, about 5 to 7 minutes. Add garlic in during the last 1 minute of cooking. Remove from pan into a small bowl and set aside.
Pound out chicken breasts until thin, or butterfly breasts. Spoon vegetable mixture into the middle. Sprinkle with cheese. Fold chicken breasts over so filling is inside. Secure with toothpicks if desired.
In a small bowl combine cumin, chili powder, onion powder, salt, and red pepper flakes (if using). Sprinkle over chicken breasts.
Wipe out the skillet you used for the vegetables and return to medium-high heat. Add remaining 1 tablespoon olive oil to the pan along with butter. Add in chicken breasts and cook for 5-7 minutes per side, or until chicken reaches an internal temperature of 165 degrees Fahrenheit.
Drizzle with lime juice before serving and garnish with freshly chopped cilantro (optional).
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Notes
BAKING INSTRUCTIONS: Instead of cooking the stuffed chicken in a skillet on the stovetop, you can also cook it in the oven instead. Place the stuffed chicken into a lightly greased 9x13 pan. Bake in a 400 degree oven for about 30 minutes, until chicken reaches an internal temperature of 165 degrees.