Preheat your oven to 375°F and line a standard 12-cup muffin tin with paper liners or grease it well. While the oven heats, dice the strawberries into 1/2-inch pieces and slice the rhubarb into 1/4-inch thick rounds. Set these fruits aside on a plate. Having everything prepped before you start mixing ensures the batter doesn't sit too long and lose its rise.

In a large mixing bowl, whisk together the flour, protein powder, baking powder, baking soda, salt, and cinnamon. Mix thoroughly to distribute the leavening agents and cinnamon evenly—this prevents lumps and ensures consistent rise and flavor throughout all the muffins.

In a separate bowl, whisk together the Greek yogurt, coconut sugar, avocado oil, milk, room-temperature eggs, and vanilla essence until smooth and well combined. The room-temperature eggs are important here—they incorporate more smoothly into the batter and create a more tender crumb. I like to use Fage 5% yogurt specifically because its higher fat content keeps these muffins moist even after a day or two.

Pour the wet ingredient mixture from Step 3 into the dry ingredient mixture from Step 2. Gently fold together with a spatula or wooden spoon just until the ingredients are combined—do not overmix. A few small lumps in the batter are fine; overmixing develops gluten and creates dense, tough muffins instead of the tender crumb you want.

In a small bowl, toss the prepared strawberries and rhubarb with the remaining 1/4 cup flour—this prevents them from sinking to the bottom of the muffins during baking. Gently fold the floured fruit into the batter from Step 4 until just combined. The fruit coating keeps the pieces evenly distributed throughout and prevents the filling from creating a soggy bottom layer.

Divide the batter evenly among the muffin cups, filling each about two-thirds full. Bake in the preheated 375°F oven for 18-20 minutes, or until a toothpick inserted into the center of a muffin comes out clean or with just a few moist crumbs. The tops should be lightly golden and spring back when gently pressed.

Remove the muffin tin from the oven and let the muffins cool in the tin for about 5 minutes before turning them out onto a wire rack to cool completely. This brief resting period allows them to set just enough to remove cleanly without breaking. Serve warm or at room temperature.