Whisk lemon-lime soda, olive oil, soy sauce, and garlic powder in a bowl and pour into a resealable plastic bag.
Add chicken breasts, coat with the marinade, squeeze out excess air, and seal the bag. Marinate in the refrigerator overnight.
Preheat grill for medium heat and lightly oil the grate.
Remove chicken from marinade and discard used marinade. Cook chicken breasts on preheated grill until no longer pink in the center and the juices run clear, 7 to 8 minutes per side. An instant-read thermometer inserted into the center should read at least 165 degrees F (74 degrees C).
