Cook pasta shells according to instructions on the package. Drain. Place on a large plate. Cool slightly.
In a large saucepan, heat up olive oil. Add garlic and saute for 2 minutes, stirring often. Add ground beef and cook until done, stirring often. Add taco seasoning, salt and pepper. Add water and simmer for 5 minutes. Add black beans, if using. Stir and cook 2 minutes. Remove from heat and cool slightly.
Preheat oven to 375 degrees F. Mix crushed tomatoes and salsa. Spread 3/4 of the sauce on the bottom of 13" by 9" casserole dish. Fill pasta shells with meat mixture and arrange over the sauce. Top with remaining sauce. Top with cheese. Bake for 18 minutes or until the dish is bubbly and the cheese is melted.
Serve pasta shells topped with chopped fresh tomatoes and green onions. Use your favorite taco toppings.