Preheat and prep. Heat your oven to 350°F (175°C). Lightly grease a small oven-safe ramekin or baking dish (about 10–12 oz capacity) with cooking spray or oil.
Blend the base. In a blender, add oats, protein powder, milk, Greek yogurt, egg, banana, baking powder, salt, vanilla, and cinnamon (if using).
Blend until smooth and pourable. The batter should be thick but not paste-like.
Taste and adjust sweetness. Give the batter a quick taste. If your protein powder isn’t very sweet, add a teaspoon or two of maple syrup or your preferred sweetener and blend again.
Stir in the chocolate. Pour the batter into your ramekin.
Gently fold in most of the chocolate chips, then sprinkle a few on top for a melty finish.
Bake. Place the ramekin on a baking sheet (for easy handling) and bake for 20–25 minutes. It’s done when the top is set, the edges are lightly golden, and a toothpick comes out mostly clean with a few moist crumbs.
Rest and serve. Let it cool for 5 minutes. Enjoy as is, or top with a dollop of yogurt, a drizzle of peanut butter, or a few extra chocolate chips.