In a large bowl, whisk together garlic, butter, brown sugar, olive oil Worcestershire sauce, Tabasco, salt and pepper.
Add duck, peppers and onions and toss to coat evenly.
Cover and refrigerate for 2 – 3 hours.
Remove duck, peppers and duck from marinade and grill on a medium-hot grill until duck breasts are medium-rare and vegetables are lightly charred.
Let duck rest for a few minutes before slicing and arranging with peppers and onions on plates.