1. Combine the cornstarch in cold water and dissolve. Set aside.
2. Mix soy sauce, pineapple juice, brown sugar, grated ginger, and garlic in small saucepan over medium-low heat; bring to a boil and simmer until sauce reduces, about 15 to 18 minutes.
3. Add cornstarch water mixture and simmer until thick, about 2 minutes. Remove from heat and set aside to cool.
4. Heat the grill. When hot, clean the grates and spray with oil.
5. Place the patties on the grill and cook on high heat for about 5 to 7 minutes on each side, or until burgers are cooked to your liking.
6. While the burgers are cooking, grill the pineapple slices for about 2 to 3 minutes on each side. Grill the onion slices.
7. To serve, place a piece of lettuce on the bottom of each burger bun. Place your grilled onions, cooked bacon, and sliced tomato onto the bun. Top with the cooked burger and 1 tablespoon of teriyaki sauce, then top with grilled pineapple.