In a bowl, combine egg white and cornstarch, and whisk until well-blended and frothy. Add chicken and let stand for about 8 to 10 minutes.
In a skillet over medium heat, heat about 2-inches deep of oil to about 350 F. Add chicken pieces and stir gently to separate. Deep-fry for about 3 to 5 minutes or until golden brown and crisp. With a slotted spoon, remove chicken and drain on paper towels. Keep warm.
Remove excess oil from pan except for about 1 tablespoon. Increase heat to medium-high heat. Add onions and bell peppers and cook, stirring frequently, for about 2 to 3 minutes or until tender yet crisp.
Add pineapples and cook for about 1 to 2 minutes or until heated through. With a slotted spoon, remove from pan and keep warm.
In a bowl, combine pineapple juice, sweet chili sauce, and cornstarch. Stir until well-blended. Add to pan and allow to boil for about 1 to 2 minutes until bubbly and thickened. Season with salt to taste.
Add chicken, bell peppers, onions and pineapples back into the pan. Gently toss to fully coat with sauce.
Transfer onto a serving platter and garnish with sesame seeds, if desired. Serve hot.