In a medium bowl, combine the dry ingredients: 1 cup all-purpose flour, 2 teaspoons baking powder, 2 ½ tablespoons cocoa powder, ½ cup turbinado raw cane sugar, and one pinch kosher salt.
Add the wet ingredients: 1 large egg, ¾ cup low-fat Greek yogurt, and 1 teaspoon vanilla extract.
Mix the wet ingredients into the dry ingredients. Spray with cooking spray or grease 6 cups of a muffin tin, then pour in the batter equally to the 6 cups (or 7 or 8, for slightly smaller cakes). Lightly spray the tops of the cakes, then bake for 15 to 20 minutes until the tops are lightly browned. Let stand in the muffin tin 1 minute, then remove to a wire rack to cool for 5 minutes.
While the cakes bake, wash the peaches and slice enough for about 2 cups into a medium bowl. Stir in 1½ tablespoons sugar and 1 teaspoon balsamic vinegar, then let stand until serving, stirring occasionally.