Dice chicken, peppers, and onion into even 2" pieces and toss with olive oil, salt, pepper, and garlic powder.
Split mixture in half and place onto two sheet pans lined with aluminum foil or a silicone baking mat.
Drain and reserve pineapple juice; add ½ of the diced pineapple pieces to sheet pans and bake at 350° for 20-25 minutes, or until chicken is done and vegetables are tender. NOTE: if you prefer veggies without any crispness, bake for 10 minutes prior to adding chicken and pineapple pieces.
Pineapple Jalapeño Sauce
To a saucepan, add remaining pineapple and juice and remaining sauce ingredients (minus the cornstarch slurry). Bring to a light simmer for 5-7 minutes, stirring frequently until sugar is dissolved and peppers are tender. Whisk in cornstarch and continuously stir for another 1-2 minutes until sauce thickens.
Notes
*If using coconut aminos is place of soy sauce, you may wish to decrease the brown sugar and add a pinch or two of salt. Coconut aminos is much sweeter in flavor than soy sauce and lacks that classic saltiness.