Bring a large pot of water to a boil. Add cauliflower and cook for 3 minutes. Remove from heat. Drain and set aside.
Heat olive oil in a large skillet over medium heat. Add onion and cook until softened. Add garlic and red pepper flakes and cook for 1 minute. Add ground beef, salt and pepper and cook until beef is browned.
Stir in tomato paste and oregano and cook for 2 more minutes. Stir in crushed tomatoes. Reduce heat to medium low and simmer for 15 minutes. Remove from heat.
Pour meat sauce over the cauliflower and stir to combine.
In a 9x13 baking dish, spread out half the cauliflower. Top with half the ricotta, mozzarella and Parmesan. Add the rest of the cauliflower and top with the remaining cheeses.