Prep the pan and oven: Heat the oven to 350°F (175°C).
Line a 12-cup muffin tin with paper liners or grease lightly.
Mix dry ingredients: In a large bowl, whisk 1 cup all-purpose flour, 1/2 cup almond flour, 1/2 cup rolled oats, 1/2 cup protein powder, 1 1/2 teaspoons baking powder, 1/4 teaspoon baking soda, and 1/4 teaspoon salt. Break up any protein powder clumps.
Mix wet ingredients: In a separate bowl, whisk 2 eggs, 3/4 cup Greek yogurt, 1/3 cup milk, 1/3 cup maple syrup, 1/4 cup melted coconut oil, and 2 teaspoons vanilla. Add 1 teaspoon lemon zest if using.
Combine: Pour wet into dry and stir gently with a spatula until just combined.
The batter will be thick. Do not overmix.
Fold in berries: Gently fold in 1 to 1 1/4 cups raspberries. If using frozen, toss them in 1 teaspoon flour first to reduce bleeding.
Portion: Divide the batter evenly among the muffin cups, filling them about 3/4 full.
Sprinkle a few extra oats on top for texture if you like.
Bake: Bake 18–22 minutes, until the tops are set and lightly golden and a toothpick comes out with a few moist crumbs.
Cool: Let muffins cool in the pan for 5 minutes, then move to a wire rack to cool completely. They firm up as they cool.