In a bowl, combine the milk, onion, saltines and seasoned salt. Crumble beef over mixture and mix lightly but thoroughly. With wet hands, shape into 1-in. balls. In a large skillet over medium heat, brown meatballs in small batches, turning often. Remove with a slotted spoon and keep warm. Drain skillet.
Drain pineapple, reserving juice; set pineapple aside. Add enough water to juice to measure 1 cup. In a bowl, combine the cornstarch, pineapple juice mixture, vinegar, soy sauce, lemon juice and brown sugar until smooth. Add to skillet. Bring to a boil; cook and stir until thickened, about 2 minutes. Add meatballs. Reduce heat; cover and simmer for 15 minutes. Add the pineapple; heat through.