Spray grill or grill pan with vegetable cooking spray and preheat over medium-high heat.

Season burgers with salt and ground black pepper to taste and grill 10 to 14 minutes, turning halfway through cooking. Place pineapple slices on grill last 5 minutes of cooking.

Serve burgers on buns spread on each side with 1 tablespoon of barbecue sauce and top with grilled pineapple, cheese, lettuce, and avocado if desired.