Preheat oven to 400 degrees. Coat a 9×9-inch baking pan with cooking spray. You can use a glass or metal pan.
Cook pasta and only cook for 6 minutes so it will not be overcooked. No need to add salt to the water! Drain and rinse in cold water. Drain again.
In a large bowl, mix together cooked pasta, cottage cheese, tomatoes, salsa, beans, and butter. Blend in egg, cumin, chili powder, garlic powder and pepper, to taste. Be sure to mix well.
Transfer pasta mixture to the baking pan. Bake casserole 20 minutes.
In the meantime, in a small bowl, mix together sour cream and scallions. Remove casserole from oven after 20 minutes and spread mixture over the top, using a rubber spatula. It’s a must to use a rubber spatula for spreading to prevent the casserole from lifting up. Next, sprinkle evenly with cheese. Place back in oven and bake about 6 minutes longer, until cheese is melted.
Remove from the oven. Let casserole rest for 10 minutes. Cut into 6 serving. This casserole freezes great!