Preheat your oven to 350°F (175°C) so it’s fully heated by the time the batter is ready. Lightly grease an 8×8-inch baking dish with oil or nonstick spray, making sure the corners and sides are well coated to prevent sticking and ensure clean slices later.

In a large mixing bowl, add the yogurt, eggs, milk, lemon juice, lemon zest, vanilla extract, and sweetener. Whisk thoroughly until the mixture is completely smooth and well combined, with no streaks of egg or yogurt remaining. This step creates a creamy, evenly flavored base for the baked oatmeal.

In a separate bowl, combine the rolled oats, protein powder, baking powder, and salt. Stir well so the protein powder and baking powder are evenly distributed throughout the oats, which helps prevent clumping and ensures even baking.

Gradually add the dry oat mixture to the wet ingredients, stirring gently with a spatula or spoon. Mix just until everything is combined and no dry pockets remain. Avoid overmixing, as this can make the baked oatmeal dense instead of soft and tender.

Gently fold in the blueberries, using light motions so they stay mostly intact and don’t bleed too much color into the batter. This keeps the oatmeal visually appealing and ensures bursts of blueberry flavor in each bite.

Pour the batter into the prepared baking dish and use a spatula or the back of a spoon to smooth the top evenly. Spread the mixture into the corners so it bakes uniformly across the dish.

Place the baking dish on the center rack of the oven and bake until the oatmeal is set in the middle and lightly golden around the edges. The center should feel firm but still slightly soft when gently pressed.

Remove the dish from the oven and let the baked oatmeal cool completely before slicing. Cooling allows it to fully set, making it easier to cut into neat portions and improving the overall texture.