Combine tequila, lime juice, orange juice, chili powder, jalapeno pepper, garlic, salt and pepper in a bowl. Toss in the chicken breasts. Refrigerate overnight.
Heat a grill with coals and brush the rack with oil to prevent the chicken from sticking.
Take out the chicken breasts from the marinade, sprinkle well with salt and pepper, and grill them skin-side down for approximately five minutes, until nicely browned.
Turn the chicken and cook for another 10 minutes, until just cooked through.