This is made in the crockpot, which keeps it really moist (the spinach helps, too). In addition to being just a darn good, traditional meatloaf, it's a good way to get kids and other spinach-haters to eat the green stuff.
Line your crockpot with tin foil so that it covers the bottom and extends all the way up the sides (you will use it to pull the meatloaf out later). In a large bowl, using your clean hands, mix all the ingredients together. Pat mixture evenly into the crockpot. Tuck the ends of the foil under the lid so it closes tightly. Cook on Low for 4-6 hours or High for 8-10 hours, or under the juices run clear when you stick a fork into the meat.