My Mom made this quite a bit growing up. It is simple and delicious. Some how the carbonation in the soda helps the chicken absorb the oil and soy sauce, making it "moist and savory."
4-6 chicken breasts
2 parts lemon-lime soda (Sprite, 7-up, Sierra Mist, etc.)
1 part oil
1 part soy sauce
Marinate the chicken in the marinade for 12-24 hours before grilling it up.