Sprinkle London broil on all sides with black pepper and place on a greased baking sheet or dish.

Preheat the oven to broil. Broil for 10 minutes on each side, until crispy brown. Let cool completely.

Reduce oven temperature to 400 degrees Fahrenheit. Line a baking sheet with aluminum foil and grease liberally with nonstick cooking spray.

Shape the prepared grits into thin patties, about two inches in diameter, and place on prepared baking sheet. You should have about 12 patties. Bake for 10 minutes. Flip over and bake an additional 10 minutes.

Heat oil in a frying pan over medium-high heat. Add grits cakes and fry for about one minute on each side, or until browned. Remove from oil and drain on paper towels.

Combine vinegar and brown sugar in a small saucepan over medium heat. Cook until sugar is dissolved and mixture is slightly reduced.

Slice cooled London broil very thinly across the grain. Meat should still be quite rare inside.

Heat additional oil in a frying pan over medium heat. Add red onion and fry until lightly browned. Remove from pan and set aside. Add London broil slices to the pan and fry on one side until lightly browned but not crispy. Turn meat over. Add two to three tablespoons of the vinegar–sugar mixture and continue cooking for one minute. Repeat with remaining slices of meat.

Combine meat and red onions. Serve on top of grits cakes.