Preheat oven to 350 °F (175 °C).

Sauté chopped onion and bell pepper in a skillet over medium heat until softened.

In a saucepan, whisk together ketchup, garlic salt, salt, pepper, Worcestershire sauce, pineapple juice, brown sugar, and flour. Heat until mixture thickens, stirring frequently.

Stir in sautéed onion, bell pepper, and pineapple chunks.

Place chicken breasts in a baking dish and pour the sweet-and-sour sauce mixture over them, coating well.

Bake uncovered for 1 – 1½ hours, until chicken is cooked through (165 °F internal temperature) and sauce is bubbly.

Let rest a few minutes before serving. Delicious over white rice or with steamed vegetables.