Brown ground beef and drain. Combine picante sauce, water and tomato sauce. Stir 1/2 C. of the sauce into the beef, along with the chilies, 1/2 C. cheese, taco seasoning and 1/2 C. onions. Mix well. Pour 1/2 C. of remaining sauce on the bottom of a 9x13-inch baking dish. Stuff cooked and drained pasta shells with beef mixture and arrange shells in the baking dish. Pour remaining sauce over shells. Bake, covered for 30 minutes at 350 degrees. Top with remaining cheese and onions. Bake an additional 5 minutes.