Preheat your oven to 350°F (175°C).
Remove the core from the cabbage and chop it into bite-sized pieces. Bring a large pot of salted water to a boil, and cook the cabbage for 5-7 minutes until tender. Drain in a colander and set aside.
In a large skillet over medium heat, add olive oil and sauté the diced onion until translucent, about 5 minutes. Add the minced garlic and cook for an additional minute.
In a mixing bowl, combine the cooked rice, sautéed onion and garlic, shredded cheddar cheese, sour cream, eggs, salt, black pepper, paprika, and crushed red pepper flakes (if using). Mix well until all ingredients are incorporated.
Gently fold the cooked cabbage into the cheese mixture until well combined.
Transfer the cabbage mixture into a greased 9x13 inch baking dish, spreading it evenly. Sprinkle the grated Parmesan cheese over the top.
Bake in the preheated oven for 30-35 minutes, or until the casserole is bubbly and golden brown on top.
Remove from the oven and let it cool for a few minutes before serving.