Preheat the oven to 400°F and line a baking tray with parchment paper.
Cut the chicken breast into bite-sized pieces ensuring even sizes for uniform cooking.
In a bowl, whisk together the egg white and cornstarch. Toss the chicken pieces in this mixture until well coated for a light crisp exterior.
Dice the red bell pepper and chop the garlic and ginger finely. Combine these with the pineapple chunks in a separate bowl.
In a small mixing bowl, stir together soy sauce, rice vinegar, honey, garlic, and ginger to form the sweet and sour sauce.
Toss the coated chicken pieces with the vegetable and pineapple mixture, then drizzle the sweet and sour sauce over everything ensuring even distribution.
Spread the mixture onto the prepared baking tray in a single layer to ensure crisping.
Bake in the preheated oven for 18-20 minutes, or until the chicken is thoroughly cooked and lightly crispy on the edges.
Remove from the oven, toss gently, and serve immediately with an optional garnish of extra chopped bell pepper if desired.