Heat oven to 350°F. Cook and drain pasta shells as directed on the box.
Meanwhile, in a nonstick skillet, cook beef over medium-high heat for 5 minutes, stirring frequently, until thoroughly cooked, and then drain. Add taco seasoning mix, 1/2 can of enchilada sauce, diced tomatoes, and 1 cup of shredded cheese; stir well until cheese is melted.
Use the remaining can of enchilada sauce and cover the bottom of an ungreased baking dish.
Fill each pasta shell with about 1 tablespoon beef mixture and place in the baking dish. Sprinkle with the remaining 1 cup cheese.
Bake 15 to 20 minutes or until heated through and cheese is melted. Serve warm.
Garnish with sour cream, cilantro, diced green onion, and/or crushed tortilla chips.
