Heat grill to medium heat. Cut 4 sheets, enough to wrap the chicken and veggies, of heavy duty foil. Place chicken on center of aluminum foil and divide the veggies and add 2-3 pineapple slices into each packet. In a bowl, whisk together bbq sauce, juice from the can of pineapple slices, soy sauce, and garlic. Spread about 2 Tablespoons of the sauce on the chicken and make sure to reserve about ¼ cup. Place chicken packets onto grill and grill for 13-15 minutes flipping at about 7 minutes. To serve carefully open packets, baste with reserve sauce and garnish with green onions.