Mix the flour and ½ teaspoon salt together. Coat the pork in the flour mixture. Sauté pork in the vegetable oil until the pork is tender, about 8-10 minutes. Remove from pan and set aside.
Drain pineapple, reserve syrup. Combine brown sugar and cornstarch. Add pineapple syrup, pineapple juice, vinegar, soy sauce and salt. Bring to a boil. Cook and stir until sauce thickens (about 3-4 minutes). Add pineapple, green pepper and onion. Cook for 2-3 minutes more. Add the pork to the sauce mixture. Serve over rice.
You can substitute fresh pineapple for the canned version, but you'll need to make a syrup with the pineapple juice. The canned pineapple works just fine.