Place chicken in shallow dish. Rub with lime juice, cumin, salt and pepper.
Cover and let marinate for at least 20 minutes and up to to 1 hour.
Heat 1 Tbsp. oil in large skillet over high heat. Cook chicken until browned on both sides, about 10 mins. per side.
Transfer to plate and keep warm.
In same skillet, heat remaining Tbsp. oil over medium high heat. Add onions, pepper and garlic. Season with salt and pepper. Cook, stirring frequently, until onions and peppers are beginning to soften, about 10 mins.
Meanwhile, wrap tortillas in aluminum foil and heat in oven until warmed through, about 10-15 minutes.
To serve, slice chicken and serve with peppers, onions and tortillas