Combine all ingredients except the jam in a large mixing bowl.
Line or grease a muffin tin then fill each cup completely. They won’t rise much during the baking process.
To add jam: Using a small spoon (dessert, baby or sugar works well), scoop a spoonful of jam onto the spoon, then press the side of your spoon into the top of the oat cup creating a divot. Smooth out with your fingers as needed. It’s super simple, no shaping required.
Cook for 25 minutes (if using jam, about 22 minutes if you skip it.)