Add the ground chicken and chopped onion to the skillet and cook, breaking up the meat with a spatula, until the chicken is cooked through and no longer pink, about 5–7 minutes.
Stir in the chili sauce (or ketchup), brown sugar, yellow mustard, salt, black pepper, and garlic powder until evenly combined.
Reduce the heat to low and simmer the mixture, stirring occasionally, for 2–3 minutes to meld flavors and thicken slightly.
Optionally toast the hamburger buns, then spoon the sloppy joe mixture onto each bun and serve immediately.
Notes
Use chili sauce for a sweeter, tangier flavor or ketchup for a milder sauce.
Cook the chicken until fully browned to ensure food safety.