In a medium bowl or measuring cup, mix the pineapple juice, brown sugar, soy sauce, ketchup, vinegar, garlic, and crushed red pepper toghether until blended.
Pour some sauce over the cut chicken to marinade it for a few minutes to a couple of hours. (You can use all the sauce if desired, if you like lots of sauce make a double batch, use orange juice if you don't have more pineapple juice)
Add double the brown sugar to make it sweeter, double the vinegar to make it tangier, double the ketchup for less umami flavor, double the soy sauce for more umami flavor and saltiness, more crushed red pepper flakes for more spice, add 2 teaspoons smoked paprika for a smokey flavor, add 2 tablespoons BBQ sauce if you're a BBQ sauce fan.
Skewer the peppers, onions, pineapple and chicken onto kabob skewers.
Cook in the oven, on a pan on the stove, on the grill, on a Blackstone griddle. Don't want to use skewers, saute the chicken and vegetables in a pan, air fryer or bake on a sheet pan. Cook or bake on medium high heat until the chicken is 165°. Heat the remaining sauce in a skillet and mix 1 cup water with 1/4 cup cornstarch and drizzle it into the simmering sauce until thick and glossy. Be sure to bring the sauce to 165° if you use any sauce that the chicken was marinating in.
Brush sauce over the chicken and vegetables to add more flavor! Make extra sauce if you want more sauce to pour over rice or noodles.