In a gallon-sized sealable plastic bag, combine pineapple juice, honey, brown sugar, soy sauce, ketchup, mustard, garlic, and onion powder. Knead bag until well-combined.
Add chicken tenderloins to marinade and knead bag to coat evenly. Refrigerate 1-6 hours to marinade.
Heat griddle to medium-high heat and coat the surface with a thin layer of olive oil.
Place chicken on griddle and cook for approximately 8-10 minutes (until internal temperature reaches 165 degrees), turning chicken every two minutes.
(Optional) Add fresh pineapple to a different part of griddle and cook for 5 minutes, turning occasionally. Serve pineapple with chicken.
