Preheat the oven to 400 F. Line a baking sheet with parchment paper and set aside.
Destem the cauliflower, remove all the leaves and discard. Holding the cauliflower with its base on the cutting board, cut right through the center of the cauliflower so that you have two even halves. Take each half and cut a steak that is 1" wide. You will end up with two 1" steaks. The remaining ends of the cauliflower can be roasted along with the steak or saved for other cauliflower recipes.
Place the cauliflower on the baking sheet and generously brush with oil. Sprinkle with garlic and bake for 30 minutes. After 30 minutes, flip the steaks and brush the underside with oil. Return to the oven and bake an additional 10-15 minutes until steaks are tender and the edges are brown.
While cauliflower steaks are baking, gently dry-toast the pine nuts over the stovetop. This takes about 3-4 minutes, shaking constant. Remove from heat and set aside.
Remove from oven. Immediately shred vegan parmesan (if using) over the warm steaks to allow it to melt. Evenly squeeze the lemon juice over the two steaks and freshly ground pepper. Top with pine nuts and parsley and serve with pasta or a large caesar salad.
Serving and Storing - Serve these cauliflower steaks alongside pasta, artisan bread, or a big Caesar salad. This recipe does not store well. They should be eaten within 30 minutes of roasting. If you have leftover cauliflower steaks, store them in an airtight container in the refrigerator for up to 3 days. To reheat, gently reheat over the stovetop with a bit of olive oil.