Dice the chicken thighs and mince the garlic. Place in a zipper bag with 1/2 cup of teriyaki sauce. Let marinate for at least 1 hour.
When you are ready to cook, preheat the Flat Top by turning the burners to medium-low and allow 10-15 minutes for heating.
As the Flat Top heats, slice the peppers, mushrooms, and onion.
Add all the sliced vegetables to one side of the Flat Top. Add the chicken to the other side and stir both occasionally. Season with salt and pepper to taste.
Once the vegetables start to become tender, mix with the chicken and top with 1/2 c. of the teriyaki sauce.
Once the chicken is cooked through, remove from the Flat Top. Garnish with sesame seeds, green onions, and the remaining teriyaki sauce, if desired!toppings!