Preheat the oven to 400°F and line a baking sheet with parchment paper.
Slice the chicken breast into bite-sized pieces. In a shallow bowl, whisk the egg whites until frothy.
Place the whole wheat breadcrumbs in another shallow dish.
Dip each chicken piece first in the egg whites, then coat evenly with the breadcrumbs.
Arrange the coated chicken pieces on the prepared baking sheet and bake for 18-20 minutes, or until golden and cooked through.
While the chicken bakes, prepare the vegetables. In a medium bowl, combine the sliced red bell pepper and pineapple chunks.
For the sauce, mix together 1/4 cup pineapple juice, 1 tablespoon low-sodium soy sauce, 1 tablespoon apple cider vinegar, 1 teaspoon honey, and 1 tablespoon ketchup until well combined.
Once the chicken is done, remove it from the oven and add it to the bowl with the vegetables, then drizzle the sweet and sour sauce over the mixture.
Gently toss everything together so that the chicken and fruit are evenly coated with the sauce.
Serve immediately and enjoy your flavorful, crispy baked sweet and sour chicken.