Add pineapple juice, soy sauce, sugar, ginger, and garlic powder to a bowl and mix well. Divide the marinade in half, and cover and store one-half of the marinade in the refrigerator. Reserve the rest of the marinade for the chicken breasts.

Place the chicken breasts in a large gallon storage bag and pour one-half of the marinade over the chicken breasts. Seal the bag, refrigerate and let the chicken marinate for at least four hours or up to 24 hours.

Remove the chicken from the refrigerator and let it come to room temperature while your grill heats up. Discard this marinade.

Take the reserved teriyaki marinade and place in a small saucepan over medium heat. Bring to a boil, then reduce the heat to low and let it simmer for 5-7 minutes. Set aside.

Set up the grill for direct grilling and preheat to high, which is 400 degrees F.

Clean the grill grates and rub the grates with a paper towel soaked in oil to prevent your chicken from sticking. I use tongs to hold the folded paper towel.

Arrange the chicken on the grill grates and baste liberally on both sides with the marinade. Grill the chicken for 5-6 minutes per side or until a meat thermometer registers 160 degrees F. when inserted in the thickest part of the chicken.

Remove the chicken from the grill and cover loosely with foil or a pot lid. Allow it to rest for about 5 minutes and to come up to 165 degrees F., which is the safe temperature for chicken. Serve immediately and enjoy.