Preheat the oven to 400. Line 12 muffin cups with paper liners, or grease with cooking spray.

In a large bowl, whisk together the flour, sugar, salt, and baking powder.

In a small bowl or measuring cup, whisk together the oil, egg, and buttermilk. Pour the wet ingredients into the dry and mix until just combined. Gently fold in the peaches.

Scoop the batter into the prepared muffin tin, filling 3/4 cup full.

To make the streusel, combine the sugar, flour, and cinnamon in a small bowl. Cut in the butter using a pastry blender or two knives, until the pieces are no larger than pea sized. Sprinkle the streusel topping over the muffins.

Bake 15-20 minutes, or until lightly browned. Let cool before serving.