Toss all ingredients except the London broil in a large freezer bag. Close the bag and give a few gentle shakes. Add the London broil and marinate in the fridge for at least 2 hours or up to 24 hours.

Preheat broiler to high and broil for 6 or 7 minutes per side. Remove from broiler and let rest, covered with foil for 10 minutes. Slice across the grain.

For grill pan :

Preheat oven to 500 degrees. Preheat a dry grill pan over high heat until screaming hot. Sear for 3 minutes on one side, flip over and put in preheated oven for about 8 – 10 minutes. Remove and let rest, covered with foil for 10 minutes.

Slice across the grain.

Heat oil in a large skillet or saucepan over medium high heat. Add the onions and cook down for about 15 minutes or until they have softened. Add the balsamic vinegar and cook until most of the liquid has evaporated. Add the water and continue to cook until the gluten free mixture has thickened, the onions are very soft and slightly caramelized and the cooking liquid has evaporated. Add salt, pepper and thyme.

Can be store covered in the fridge for up to a week.