For BBQ Sauce: Heat butter over low heat in saucepan, add shallots and sauté until tender and golden. Remove from heat. Add in rest of ingredients, stir well to combine, return to heat, and bring to a simmer. Simmer for 5 minutes over low heat, stirring. Set aside with lid tilted.
For Chicken: Butterfly, pound, and seasoning both sides of chicken breasts. Heat grill to medium. Spray tops of chicken with butter-flavored no-stick spray, and place filets onto grill sprayed side down. Care fully, lightly, spray tops. Close lid and grill until light golden brown and grill marks. Turn, coat with some sauce, close lid and grill again. (3 - 4 minutes each time.) Turn, and start slathering with sauce, turning and basting with lost of sauce until done, about another 2 - 4 minutes on each side, depending on thickness and how hot your grill is. When done inside, remove to plate and top each with a little more sauce of desired.
Butter insides of buns, and grill until toasted. Place chicken onto bottom buns, top with lettuce, tomato, bacon and onion. Place on tops and enjoy!!