beef tenderloin, thinly sliced, marinade with 1 Tbsp oyster sauce and 1 tsp sweet soy sauce, mix well, set aside for at least 30 minutes • vegetable oil • garlic, minced • onion, thinly sliced • red bell pepper, sliced • green bell pepper, sliced • sweat soy sauce • oyster sauce • salt • sugar • freshly ground black pepper • water