01 - Preheat oven to 350°F. Lightly grease an 8x8-inch baking dish with cooking spray or butter.
02 - In a large mixing bowl, whisk Greek yogurt, eggs, almond milk, maple syrup, lemon juice, lemon zest, and vanilla extract until completely smooth and well combined.
03 - Add oats, protein powder, baking powder, and salt to the wet mixture. Stir until just combined, being careful not to overmix.
04 - Gently fold blueberries into the batter using a spatula, taking care not to crush the fruit.
05 - Pour mixture into the prepared baking dish and smooth the top with a spatula. If using, sprinkle sliced almonds and chia seeds evenly over the surface.
06 - Bake for 35 minutes or until the center is completely set and the top is golden brown. A toothpick inserted into the center should come out clean.
07 - Let the breakfast bake cool for 5 to 10 minutes before slicing into 6 equal portions. Serve warm or at room temperature.