Remove leaves and trip stem end of the cauliflower leaving core intact.  Using a large knife cut out 1/2" steaks from the center of the cauliflower, and cut any remaining smaller steaks out too.

Preheat oven to 400 degrees F.  Heat 1 tablespoon oil in a large heavy skillet.  Cook steaks in hot pan about 2 minutes per side until they are golden brown.  Remove to a baking sheet.  Halfway through cooking add another tablespoon oil.  Once all steaks are browned place the pan in the oven for about 15 minutes to ensure the steaks are tender.

Meanwhile, warm up your tomato sauce and prepare gremolata.

Finely chop walnuts, place on a dry baking sheet. Bake 5-7 minutes until lightly toasted, stirring once or twice. Cool.  Finely chop parsley and place in a small bowl.  Add zest and cooled walnuts, garlic, salt and pepper.

When ready to serve, spoon tomato sauce on to a plate, top with cauliflower steak and sprinkle with gremolata.