Brown and drain the ground beef. In a large bowl, mix beef with the can of beans and package of taco seasoning. In a small bowl, mix water and salsa. Fill each shell with the meat mixture using a small spoon or large cake decorating device if available. Arrange the shells in a microwave safe baking dish (like a rectangular glass casserole dish) and pour the water/salsa mixture over the shells. Cover dish with plastic wrap leaving a corner open to vent and microwave on HIGH for 10 minutes. (if your microwave does not have a turn table you should rotate the dish half way through for even cooking) Remove from microwave using pot holders and carefully pull the plastic wrap back. Using a spatula or fork turn all the manicotti over in the dish. Recover the dish and microwave on MEDIUM (or 50%) for an additional 20 minutes, until the shells are al dente (tender but firm). Remember to rotate the dish every 5-10 minutes if your microwave does not turn automatically. While shells are cooking, mix the sour scream in a small bowl to make creamy, adding the scallions and black olives if desired. When manicotti is done, pour this mixture over top of shells and sprinkle cheese over mixture. Microwave uncovered for 2 minutes on medium-high (80%) until cheese is melted. Enjoy!