Preheat oven to 350 degrees. Spray a nine by nine-inch square baking pan with nonstick oil. Set aside.
Place nut butter in microwave to warm it up and loosen the texture (about 30-45 seconds from room temperature).
Meanwhile, combine oats, flax meal, protein powder, cinnamon, sea salt, apple, walnuts, and dried cranberries in a large mixing bowl.
Add milk, pumpkin puree, warmed nut butter, maple syrup, melted butter, and vanilla extract to a bowl and mix until uniform.
Add wet mixture to dry and stir until there are no dry pockets left in the mixture. Spread into prepared baking pan. Bake in preheated oven for about 35 minutes or until top of oatmeal is firm when pressing down (but not hardened) and a toothpick inserted into the oatmeal comes out dry.
Cool to room temperature before slicing into nine bars. Store refrigerated in an airtight container. Keeps for about one week.