Prepare the Ingredients: Finely dice one onion and one bell pepper; set aside. Grate Swiss and cheddar cheese until you have a decent amount for topping.

Cook the Pasta: Bring a large pot of salted water to a boil and add your pasta, cooking for 2 minutes less than package instructions. Drain and set aside.

Sauté the Vegetables: In a large skillet, melt 2 tablespoons of butter over medium heat. Add the diced onion and bell pepper, sautéing for 5-7 minutes. Add oregano, garlic powder, salt, pepper, and smoked paprika, cooking for another 30 seconds.

Combine Ingredients: In a large mixing bowl, fold the sautéed vegetables into the cooked pasta. Add crab meat and sour cream, mixing gently until evenly coated.

Assemble the Casserole: Transfer the mixture to a 9x13-inch baking dish, spreading it evenly. Top with grated cheese.

Bake the Dish: Preheat oven to 350°F and bake for approximately 20 minutes until cheese is melted and bubbly.

Rest and Serve: Let the casserole rest for 2-3 minutes. Garnish with green onions before serving.