Preheat oven to 375°F. Coat a 9x13 baking pan with olive oil and line with parchment paper.
Cut apples in half and remove core. Grate apple into a large bowl. Add oats, pecans, flax seed, brewer's yeast, baking powder, salt, and frozen blueberries.
In a medium, mix together milk, yogurt, eggs, maple syrup, and vanilla extract. Stir into oat mixture.
Transfer to baking pan and sprinkle with cinnamon.
Bake until firm and golden brown, around 60-70 minutes. Cool for 10 minutes before serving.