Trim the excess fat from the pork steaks, and place them in a large shallow container.
Drain the pineapple (if using fresh, just sub a can of pineapple juice in the marinade), reserving juice or syrup. Set pineapple slices aside.
Combine pineapple juice/syrup, onion, soy sauce, oil, corn syrup, and ginger in a small saucepan, stirring well. Cook, uncovered, over medium heat for 10 minutes, stirring frequently. Pour over the pork steaks. Cover and refrigerate for at least 8 hours, turning steaks occasionally if possible.
Remove the steaks from the marinade, reserving marinade. Grill steaks over low to medium coals for 35 minutes or until the desired degree of doneness. Turn and baste occasionally with the marinade.
Grill the pineapple slices over medium coals for 1 minute on each side. Garnish the pork steaks with the pineapple slices.