Combine the tequila, lime juice, orange juice, chili powder, jalapeno pepper, garlic, salt, and pepper in a large bowl. Add the chicken breasts. Refrigerate overnight.
Heat a grill with coals and brush the rack with oil to prevent the chicken from sticking. Remove the chicken breasts from the marinade, sprinkle well with salt and pepper, and grill them skin-side down for about 5 minutes, until nicely browned. Turn the chicken and cook for another 10 minutes, until just cooked through. Remove from the grill to a plate. Cover tightly and allow to rest for 5 minutes. Serve hot or at room temperature.