Preheat your oven to 425°F and line a baking sheet with parchment paper.
Cut the chicken breast into bite-sized pieces. In a bowl, whisk the egg white and add the cornstarch. Toss the chicken pieces in this mixture until evenly coated.
In a separate shallow dish, add the panko breadcrumbs. Lightly press the chicken pieces into the breadcrumbs so they adhere well.
Place the breaded chicken pieces on the prepared baking sheet in a single layer. Bake in the preheated oven for 15-18 minutes, turning halfway, until the chicken is cooked through and the coating is crispy.
Meanwhile, prepare the sweet and sour sauce by combining pineapple juice, rice vinegar, honey, soy sauce, minced garlic, and grated ginger in a small saucepan. Bring the mixture to a simmer over medium heat and cook for 3-4 minutes until slightly thickened.
In the last few minutes of baking, add sliced bell pepper to the baking sheet for a burst of color and extra flavor, if desired.
Once the chicken is done, drizzle the sweet and sour sauce over the crispy pieces. Toss gently to ensure even coating.
Serve immediately and enjoy your balanced, crispy baked sweet and sour chicken.