Brown beef with onions, cook shells. Spread a thin layer of enchilada sauce on bottom of pan. Using an ice cream scooper (so they all have the same size) spoon meat mixture into cooked shells, along with a pinch of cheese. Roll the shells, being sure to keep the roll tight. Place rolled shells into pan. Once you have filled the pan with enchilada rolls, pour remaining sauce onto shells. Make sure its evenly distributed. Cover the rest with cheese. Spread black olives and/or green onions on top if desired. Cook at 350F for 45 minutes.