Preheat oven to 350 degrees. Spray a 12-count cupcake pan with nonstick oil spray and set aside.
Place nut butter in the microwave to warm it up and loosen the texture (about 30-45 seconds).
Meanwhile, mix old fashioned oats, flax meal, and sea salt together in a large bowl.
Add in warmed almond butter, milk, protein powder, maple syrup, and vanilla extract. Stir until uniform and no dry pockets remain.
Divide mixture into five bowls to make the different oatmeal flavor variations. Two bowls should have slightly more of the batter as you'll divide each into three cups. The other bowls will each be divided into two cups.
Add each of the flavor variations into its own bowl of base mixture and stir to combine.
Transfer prepared mixtures into prepared cupcake pan. Smooth down the tops of the mixture in the pan.
Bake for about 25 minutes or until oatmeal muffins are golden brown and tops are firm (but not dry and hardened) when pressed down.
Cool to room temperature before removing from cupcake pan.