Step 1: In a medium skillet over medium high heat, brown ground beef. Drain off any excess liquid and stir in the taco seasoning mix and ¾ cup of water. Bring to a boil, reduce heat and simmer for 5 minutes (or until the ground beef is fully cooked), stirring occasionally.
Step 2: Meanwhile, cook elbow macaroni according to package directions. While the elbow macaroni is cooking, melt butter in a medium saucepan over medium heat. Stir in flour, salt and pepper.  Cook for 2-3 minutes awhile stirring. Slowly add the milk and cook while stirring until the mixture becomes somewhat thick. Stir in cheese until melted. Remove from heat. Drain the elbow macaroni and add it to the cheese sauce. Stir to coat.
Step 3: Place a little of the taco meat into each hard shell taco and top with macaroni and cheese and green onions.