Add vegetable oil to a large skillet, and add chicken and brown over medium heat. Drain and set aside.
Drain pineapple, saving the juice. Add water to the juice to measure 1 cup; pour liquid into the skillet. Add another ⅓ cup of water, vinegar, soy sauce, brown sugar, and cornstarch.
Cook over medium heat until thick, stirring constantly. Add the pineapple, chicken, and peppers.
Simmer, uncovered until heated through, about 20 minutes. Serve over rice and chow mein noodles.