Very generously spray the slow cooker or use a liner.
Add oats and salt to the slow cooker. Add the can of coconut milk to a a 4 cup measuring cup, and add enough water to make 4 cups of liquid total. (I don’t have a four-cup measuring cup, so I add coconut milk to a two cup measuing cup, top off with water to the two-cup mark, and then add 2 full cups of water.)
Stir together and cook on low for 7 to 8 hours or on high for 3 1/2 to 4 hours.