Preheat your oven to 425°F. Line a baking sheet with parchment paper.
In a bowl, whisk together the egg white and cornstarch. Cut the chicken breast into bite-sized pieces and gently toss them in the mixture until evenly coated.
Place the coated chicken pieces on a plate and set aside. In another bowl, combine the pineapple juice, apple cider vinegar, low-sugar ketchup, garlic powder, and a pinch of salt to create the sweet and sour sauce.
In a separate bowl, mix the chopped bell pepper, zucchini, and red onion with olive oil, and season lightly with salt if desired.
Spread the vegetables on the prepared baking sheet and roast in the preheated oven for 15 minutes.
While the vegetables roast, pan-sear the chicken in a non-stick skillet over medium-high heat. Cook the chicken for about 4-5 minutes on each side until it becomes crispy and golden.
Once the chicken is cooked, pour the sweet and sour sauce over the chicken in the skillet. Allow the sauce to warm and coat the chicken, cooking for an additional 2 minutes.
Remove the vegetables from the oven. Plate the roasted vegetables and top with the crispy sweet and sour chicken. Garnish with any extra seasoning or green onion if desired, and serve immediately.