Combine the oats, brown sugar, milk, water, and salt in a large saucepan over medium heat. Bring to a boil.
3 cups quick-cooking oats, ¼ cup brown sugar, 4 cups milk, 2 cups water, 1 pinch salt
Reduce heat to medium-low, and cook for 2-3 minutes.
Let the oatmeal cool slightly.
Grease two 12-cup muffin tins with cooking spray or line with silicone or parchment muffin liners.
Divide the cooked oatmeal between the muffin tin cups.
Sprinkle desired toppings over each oatmeal cup.
Cover with plastic wrap and place in the freezer for several hours, or until frozen.
Once frozen, remove the frozen oatmeal cups and place in a freezer-safe container.
Reheat in the microwave for 1-3 minutes, or until heated through, adding additional liquid as needed.
Notes
Oats: You can substitute old-fashioned oats, but the cooking time will be longer.
Brown sugar: Granulated sugar will also work. I like the caramel tones in the brown sugar, but you can sue what you'd like. Also, free free to adjust the sweetness to your tastes.