1) Combine the tequila, lime juice, orange juice, chilli powder, jalapeno pepper, garlic, salt, and pepper in a large bowl. Add the chicken breasts. Refrigerate overnight.
2) Preheat a barbecue or griddle and brush the rack with oil to prevent the chicken from sticking.
3) Remove the chicken breasts from the marinade, sprinkle well with salt and pepper, and griddle 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.
4) Serve hot or at room temperature.