♦ Arrange meat in a single layer in a glass baking dish or in a big zip-lock bag.
♦ Whisk together oil, soy sauce, ketchup, vinegar, pepper, garlic, and pineapple juice.
♦ Pour over meat and turn to coat.
♦ Cover or seal, refrigerate and let marinate for 3-6 hours, turning meat once or twice.
♦ When ready to grill, remove meat from marinade and add the pineapple slices to marinade.
♦ Grill meats to desired doneness.
♦ The last few minutes, grill the pineapple slices till lightly browned.