Beefy Mac Casserole

Here is an awesome and easy casserole for a great meal. I like it with a simple side salad and some green chili cornbread. Great for dinner in these early fall evenings.
8 ounces elbow macaroni or small shells, cooked, drained
2 tablespoons olive oil
1 cup chopped onion
2 short ribs celery, chopped
1 green bell pepper, chopped
1/2 red bell pepper, chopped
2 medium cloves garlic, minced
1 pound extra-lean ground beef
2 teaspoons Cajun seasoning
2 cans (14.5 ounces each) tomatoes, undrained, diced
2 tablespoons tomato paste
1/2 teaspoon salt, or to taste
1/8 teaspoon black pepper, or to taste
3 cups shredded Cheddar cheese, divided
Preparation:
Heat olive oil in a large saucepan or Dutch oven over medium heat; add onion, celery, green and red pepper, and garlic. Continue to sauté the vegetables, stirring frequently, until the chopped onion is tender. Add ground beef and continue cooking, stirring, until beef is browned. Add the Cajun seasoning, tomatoes, and tomato paste. Stir to blend well and bring to a simmer. Reduce heat to low and simmer for 10 minutes. Stir in the cooked and drained macaroni and 2 cups of the shredded cheese, along with salt and pepper, as desired. Transfer to a lightly greased 13x9-inch baking pan. Cover with foil. At this point, the casserole may be refrigerated for a few hours or overnight.
Bake the covered casserole in a 350° oven for 20 to 25 minutes, or until hot and bubbly (if it is cold from the refrigerator, it may take longer). Top with the remaining cup of cheese and cook, uncovered, for 5 to 10 minutes longer.
Serves 6 to 8.