Drain pineapple, reserving all the juice in small bowl. Add soy sauce, rice vinegar, garlic powder, ginger and cornstarch to bowl; stir until smooth. Set aside.
Heat 1 tablespoon of the oil in large skillet on medium-high heat. Add chicken; stir fry 5 minutes until browned. Remove from skillet. Heat 1 tablespoon of the remaining oil in skillet. Add onion and bell pepper; stir fry 5 minutes or until tender-crisp.
Stir soy sauce mixture. Add to skillet; stirring constantly, bring to boil on medium heat and boil 1 minute or until sauce is slightly thickened. Add chicken and pineapple; stir fry 2 minutes or until heated through. Spoon sweet & sour chicken into large bowl. Stir in cilantro. Set aside. Wipe skillet clean.
For each quesadilla, sprinkle 1/4 cup cheese over half of 1 tortilla. Layer with 2/3 cup sweet & sour chicken and additional 1/4 cup cheese. Fold over. Heat 1 teaspoon of the remaining oil in same skillet on medium heat. Add 1 quesadilla; cook 2 minutes per side or until lightly browned and cheese is melted. Repeat with remaining quesadillas and oil. Cut quesadillas into wedges.