* Roast Beef should be thinly sliced and there should be 8 to 10 slices. Mix catsup, brown sugar, lemon juice, worcestershire sauce, mustard, onion salt, and pepper in 2-cup glass measure. Microwave uncovered on high (100%) 1.5 minutes; stir. Microwave to boiling, 1 to 2 minutes. Layer half the beef slices and half the sauce in 1 litre casserole; repeat. Cover and microwave on high (100%) until hot and bubbly, 1.5 to 2.5 minutes. Place bottom halves of buns on serving plate. Top with beef and reamining bun halves. Microwave uncovered on high (100%) until buns are hot, 30 seconds to 1 minute.