1. Preheat oven to 400' F. Put a sheet of parchment paper on a baking sheet and spray with non stick spray.
2. Cut off the root / bottom end of the head of cabbage. Remove as much of the core as you can. Put it on the cutting board so that the flat end is on the cutting board and the head is standing up. Cut top to bottom into 1 in thick slices of cabbage. Place flat on the baking sheet.
3. In a bowl, whisk together the olive oil, garlic, pepper and lemon juice. Brush over one side of the cabbage steak and flip the cabbage over and brush the other side.
4. Roast the cabbage in the oven for 25 - 30 minutes or until crispy at the edges and tender in the center. Halfway through the baking time, rotate the pan. No need to flip the cabbages.
5. While the cabbages roast, toast the walnuts. Add the walnuts onto a small baking sheet (no oil/grease) and place in the oven for about 5 minutes. Pay close attention so they do not get too done. Remove from oven and pan, and allow to cool then chop the walnuts into pieces.
6. Once the cabbage is roasted, remove them from the oven and sprinkle them with the walnuts. Squeeze more lemon juice on them if desired. Serve hot.