Bring the water to a boil. Add the pasta and cook, stirring frequently to avoid sticking together. Cook for 10 minutes or until the pasta has reached the desired degree of doneness. Drain the pasta (reserving some water for the sauce) and set aside.
Toss the cauliflower in the oil. Place the cauliflower on the baking sheet and bake for 10-15 minutes until fork tender and caramelized. Remove from the oven and set aside.
Heat olive oil in a medium skillet over medium heat. Add garlic and red pepper flakes; cook for 30 seconds. Add roasted cauliflower and cook for 2-3 minutes to heat through. Add pasta, chopped parsley and walnuts; Stir to combine. Season with salt and pepper, and deglaze with the pasta water. Serve topped with grated cheese.