Preheat the oven to 350°F (175°C).
Line a muffin pan with muffin liners.
In a bowl, combine all wet ingredients (Greek yogurt, water, egg white, oil, applesauce, vanilla extract, and vinegar) and mix until well blended.
In a separate bowl, combine all dry ingredients (flour, protein powder, sugar, cinnamon, baking powder, baking soda, and salt). Sift the flour to remove any lumps.
Create a well in the center of the dry ingredients and pour in the wet mixture.
Gently fold the wet ingredients into the dry ingredients until just combined. Avoid overmixing; it’s okay if the batter has a few lumps.
Pour the batter into the lined muffin pan.
Bake in the preheated oven for 17-20 minutes, or until a toothpick inserted into the center comes out clean.
Allow the muffins to cool slightly before removing them from the pan.