Preheat the oven to 375°F and line a 12-cup muffin pan with paper liners. Dice the peaches into small pieces and lightly coat them with flour so they stay evenly distributed while baking.
Whisk together the flour, baking powder, baking soda, salt, and cinnamon in a large bowl until fully combined. This helps the muffins rise evenly and keeps the texture light.
In a separate bowl, whisk the eggs, sugars, melted butter, Greek yogurt, and vanilla extract until smooth and creamy. Mixing thoroughly at this stage creates a moist and balanced batter.
Fold the wet ingredients into the dry ingredients gently until just combined, then carefully fold in the peaches. Avoid overmixing so the muffins stay soft and tender after baking.
Divide the batter evenly into muffin liners, filling each about three-quarters full. Sprinkle coarse sugar on top for a crisp bakery-style finish.
Bake for 20 to 22 minutes until golden brown and a toothpick inserted in the center comes out with a few moist crumbs. Cool for 5 minutes before transferring to a wire rack.