Drain pineapple, reserving juice; set pineapple chunks aside. Combine reserved juice, cornstarch, and next 3 ingredients; set aside.
Coat a large nonstick skillet or wok with cooking spray, and add oil. Place over medium-high heat until hot. Add green pepper and onion; stir-fry 2 to 3 minutes or until crisp-tender. Add shrimp; stir-fry 2 to 3 minutes or until shrimp turn pink.
Stir cornstarch mixture and pineapple chunks into shrimp mixture. Cook over medium heat, stirring constantly, until mixture is thickened and bubbly. Serve immediately.