"Caramelized" in quotes because they don't turn dark brown and thus aren't appropriate as a condiment, but if you want that unmistakable sweet flavor in your slow-cooker marinara sauce or Beef Stroganoff, give this a try instead of babysitting a skillet for up to an hour. If the crock from your slow cooker fits in your microwave oven, it means one less pan to wash.
Pile as many shoestring-cut onions as will fit into a microwave-safe casserole or slow cooker crock and cook uncovered for 10 minutes on high power in the microwave oven. Stir and repeat until the onions are limp and yellow, and there's no residual water at the bottom of the vessel (about 3 to 4 cycles). Add the rest of your recipe ingredients and finish as usual.