Preheat your oven to 425°F and line a baking sheet with parchment paper.
Slice the chicken breast into bite-sized pieces ensuring even thickness for consistent baking.
In a shallow bowl, whisk the egg white until slightly frothy. In another bowl, place the panko breadcrumbs.
Dip each chicken piece first in the egg white, allowing excess to drip off, then coat thoroughly with panko breadcrumbs.
Place the coated chicken pieces on the prepared baking sheet, spacing them evenly.
Bake in the preheated oven for about 15-18 minutes or until the chicken is cooked through and the coating is crisp.
While the chicken is baking, prepare the sweet & sour sauce. In a small saucepan over medium heat, combine the pineapple chunks, rice vinegar, tomato ketchup, soy sauce, cornstarch, and sesame oil.
Stir continuously until the sauce simmers and thickens slightly, about 3-4 minutes. For a smoother sauce, you can mash the pineapple chunks with the back of a spoon.
Once the chicken is done, drizzle the sweet & sour sauce over the crispy baked chicken or serve it on the side as a dip.
Garnish with a sprinkle of chopped green onions or sesame seeds if desired and enjoy!