Preheat oven to 375 F and spray square 9 x 9 baking dish with cooking spray. Set aside.

In a large bowl, add eggs, milk, olive oil, baking powder, salt, and pepper and whisk to combine.

Add oat flour and stir with a spatula.

Then add spinach, feta cheese, parmesan cheese, green onion, dill, and garlic and stir until thick batter forms.

Transfer mixture into the prepared baking dish, level with a spatula, and bake uncovered for 40 minutes or until a toothpick inserted in the center comes out clean.

Remove from the oven and let cool for 30 minutes.

Transfer brownies onto a cutting board and cut into 9 squares.

Enjoy warm or cold with a side salad.