Chop the chicken into roughly 1-inch pieces and pat them dry.

Mix flour, corn starch, and salt on a shallow plate. Whisk the egg until smooth in another bowl.

Coat the chicken pieces in the egg mixture, then the flour blend, ensuring even coverage.

Heat vegetable oil in a large skillet and cook the chicken in batches over medium heat until golden brown and cooked through.

Clean the skillet if needed, reheat, and stir-fry sliced onions and bell peppers until slightly tender. Remove and set aside.

In the same skillet, combine ketchup, rice vinegar, sugar, garlic, and sesame oil. Bring to a gentle boil, then simmer until thickened.

Add the chicken, vegetables, and pineapple to the skillet. Toss everything to coat in the sauce, then remove from heat.

Serve over rice and enjoy!