Preheat your oven to 350°F (175°C) and prepare a muffin tin with liners or cooking spray.

In a mixing bowl, whisk together the flour, sugar, baking powder, salt, and cinnamon until well combined.

In a separate bowl, beat the egg and stir in the milk and melted butter or oil until well blended.

Pour the wet ingredients into the dry ingredients and stir gently until just combined.

Fold in the diced peaches into the batter, ensuring even distribution without overmixing.

Spoon the batter into the muffin tin, filling each cup about two-thirds full.

Bake for 20-25 minutes until golden brown and a toothpick comes out clean.

Cool in the tin for 5 minutes, then transfer to a wire rack to cool completely.