01 - Preheat oven to 350°F and lightly grease an 8x8-inch baking dish with cooking spray or butter.
02 - Whisk Greek yogurt, eggs, almond milk, maple syrup, lemon juice, lemon zest, and vanilla extract in a large bowl until completely smooth and incorporated.
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, taking care not to crush them if using fresh berries.
05 - Pour mixture into prepared baking dish and smooth surface with spatula. Sprinkle sliced almonds and chia seeds evenly over top if using.
06 - Bake for 35 minutes until center is set and top is golden brown. A toothpick inserted in center should come out clean.
07 - Allow to cool for 5-10 minutes before slicing into squares. Serve warm or at room temperature.