If you like oatmeal, try overnight oats. Add some water, touch of maple syrup, your favorite fruit, dash of salt, and put it in the fridge. You can make a week's worth at a time, and try different recipes to see what you like. I went through a phase where I tried all sorts of recipes, not all vegan.
You can add other grains, too. Barley worked surprisingly well, but chia seeds had that gelatinous texture I don't care for. Pumpkin seeds, cashew pieces, and poppy seeds were all good. You can also stir in peanut butter, nutella, sunbutter, or cookiebutter if you want to make it more of a treat.