Prep the pan: Heat the oven to 350°F (175°C). Line a 12-cup muffin tin with liners or grease lightly.
Mix the dry ingredients: In a large bowl, whisk the flour, protein powder, baking powder, baking soda, salt, and lemon zest until well combined.
Whisk the wet ingredients: In a separate bowl, whisk the eggs, Greek yogurt, milk, honey, oil, vanilla, and lemon juice until smooth.
Combine gently: Pour the wet mixture into the dry ingredients. Stir with a spatula until just combined.
The batter should be thick but scoopable. Do not overmix.
Fold in raspberries: If using, toss raspberries with 1–2 tsp flour to coat. Gently fold them into the batter, keeping as many berries whole as possible.
Fill the tins: Divide the batter evenly among the muffin cups, filling about 3/4 full.
Sprinkle a pinch of coarse sugar or oats on top if you like.
Bake: Place on the center rack and bake for 18–22 minutes, or until the tops are set and a toothpick comes out with a few moist crumbs (avoid poking a berry pocket).
Cool: Let muffins cool in the pan for 5 minutes, then transfer to a wire rack. Cool completely for best texture.
Serve: Enjoy warm or at room temp. A little smear of almond butter is great if you want extra protein and healthy fats.