Preheat your oven to 425°F and line a baking sheet with parchment paper.
Trim any excess fat from the chicken breast and pat dry with a paper towel. Cut the chicken into bite-sized pieces.
In a shallow bowl, whisk together the almond flour and the egg white until you achieve a smooth, slightly sticky coating mixture.
Toss the chicken pieces in the almond flour mixture until they are evenly coated.
Place the coated chicken pieces on the prepared baking sheet in a single layer.
Bake the chicken for 18-20 minutes, flipping halfway through, until the chicken is cooked through and the coating is crisp.
While the chicken bakes, prepare the sweet and sour sauce by combining pineapple chunks, diced bell pepper, sugar-free ketchup, rice vinegar, soy sauce, and cornstarch in a small saucepan.
Heat the sauce over medium heat, stirring occasionally, until it thickens slightly, about 4-5 minutes.
Once the chicken is done, toss the crispy pieces in the warm sweet and sour sauce or serve the sauce on the side as a dip.
Plate and enjoy your Crispy Baked Sweet and Sour Chicken!