Preheat your oven to 400°F. Line a baking sheet with parchment paper to prevent sticking.
Pat the chicken breast dry. Using a food processor or a rolling pin, lightly pound the chicken to ensure even thickness for baking.
Place the panko breadcrumbs in a shallow dish. Lightly season the breadcrumbs with a pinch of salt and pepper if desired.
Coat the chicken breast evenly with the panko breadcrumbs, pressing gently to adhere the crumbs to the surface.
Place the breaded chicken on the prepared baking sheet and bake for 18-20 minutes or until the chicken is cooked through and the coating is crisp.
While the chicken bakes, prepare the sweet and sour sauce. In a small saucepan, combine the pineapple chunks, red bell pepper slices, soy sauce, rice vinegar, brown sugar, and cornstarch.
Heat the sauce over medium heat, stirring frequently. Allow the sauce to simmer for 3-5 minutes until it thickens slightly.
Once the chicken is done, remove it from the oven. Drizzle the warm sweet and sour sauce over the crispy chicken, or alternatively, toss the chicken pieces in the sauce to ensure even coverage.
Serve immediately while hot, and enjoy your crispy baked sweet and sour chicken.