Preheat and prep: Heat oven to 350°F (175°C). Grease an 8x8-inch baking dish with cooking spray or a little butter.
Blend the base: In a blender, add cottage cheese, Greek yogurt, eggs, honey or maple, vanilla, lemon zest, cinnamon, baking powder, salt, and rolled oats.
Blend until mostly smooth. A few oat flecks are fine.
Fold in berries: Pour the mixture into a bowl and gently fold in 1.5 cups of blueberries. If using frozen, don’t thaw; toss them with a teaspoon of oat flour or regular flour to reduce bleeding, if you like.
Fill the pan: Transfer to the prepared dish.
Scatter the remaining blueberries on top for a pretty finish.
Bake: Bake for 35–45 minutes, until the center is set and the edges are lightly golden. A toothpick should come out mostly clean with a few moist crumbs.
Rest and slice: Let it cool for 10–15 minutes. It will firm up as it cools.
Slice into squares.
Serve: Enjoy warm or chilled. Top with a spoon of yogurt, a drizzle of honey, or a few extra berries if you want.