Drain pineapple juice into a small bowl; add teriyaki sauce. Place 3 Tablespoon in a resealable plastic bag. Add pineapple and rotate to coat; set aside. Shape beef into four patties; place in a 20 cm square baking dish. Pour the remaining teriyaki sauce mixture over patties; marinate for 5-10 minutes, turning once. In a skillet, saut onion in butter until tender, about 5 minutes. Grill or broil burgers until no long pink. Place pineapple on grill or under broiler to heat through. Layer lettuce and onion on bottom of buns. Top with burgers, cheese, pineapple and bacon. Replace tops; serve immediately.