Mix the lemon juice, tequila, pepper flakes, chili powder, and garlic in a medium-sized plastic container. Place the steak in the container, cover, and marinate in the refrigerator for at least 45 minutes.
Heat canola oil in a large nonstick saute pan over medium heat. Add bell peppers and onion and saute until crisp tender. Remove from pan, set aside, and keep warm. Remove steak from marinade and discard marinade. Saute steak in the saute pan for about 5 minutes on each side or until cooked through. Remove steak from the pan and slice into thin strips. Return steak strips, bell peppers, and onion to pan and warm through for about 1 minute. Season with salt and pepper, to taste. Divide steak mixture evenly among the warmed tortillas. Garnish each with 1/4 cup cilantro and serve.