Mince garlic in a food processor, then add kale, hemp seeds or toasted walnuts, lemon juice, cheese if using, red pepper flakes if using, salt and pepper. Turn on the food processor and gradually drizzle in the oil until your pesto reaches your desired consistency. Scrape down the sides of the food processor as needed, season to taste and add more oil if needed. Finish and set aside.
Prepare the cauliflower steaks.
Preheat a grill pan over medium-high heat.
Cut cauliflower head into 3 to 4 steaks, and season with olive oil, lemon juice, salt and pepper if preferred. Cook the cauliflower steaks for 4 to 5 minutes on each side, until the bottom begins to char. Remove cauliflower steaks from heat and plate with kale pesto, chili flakes if desired, chopped parsley or basil, and crushed walnuts. Enjoy!