In a small saucepan, whisk together maple syrup, maple extract, brown sugar, oil, garlic, lemon juice, salt and pepper over medium-high heat. Bring to boil, whisking occasionally until sauce begins to thicken, about 1-2 minutes.
Remove marinade from heat and add thyme. Allow to cool slightly, about 5 minutes.
Place chicken in a large bowl and pour maple marinade over top.
Cover and place in refrigerator for 30 minutes to marinate.
Preheat George Foreman grill by plugging it in, or setting it to MAX, 400°F or setting 4.
Remove chicken, discarding thyme, and place on preheated grill. Grill for 6-10 minutes (depending on thickness), or until chicken reaches internal temperature of 165°F.
Note: if grilling on Indoor/Outdoor grill, grill for 10 minutes per side.
Serve hot with your favorite vegetable and starch.