Cut chicken into 6-8 smaller pieces (it grills faster and you can coat more sauce on the chicken when it's in smaller pieces.) Place chicken in an airtight container and set aside.
Combine remaining ingredients (except for the cornstarch!) in a 2-cup measuring cup and whisk until smooth. Microwave for 3 minutes. Sauce will boil and reduce slightly. Pour half into the container with the chicken. Let marinate for 2-4 hours.
Take 2 TBSP of sauce from the measuring cup and combine with the cornstarch in a small bowl. Stir until smooth, then whisk back into the measuring cup with remaining sauce. Microwave an additional 2 minutes. Set aside until it's time to grill.
Grill chicken over medium heat, coating sauce on each side as you cook. Chicken will be done with the internal temperature reaches 165 degrees F. I reserved a small amount of sauce to brush on right after it was taken off the grill to give it a nice glazed look.
If you grill pineapple, only brush a small amount of sauce on as it's fairly strong. You don't want to overpower the taste of the pineapple.