1. Preheat the oven to 375. Spray a large muffin tin and a mini muffin tin with non-stick cooking spray or line with paper or foil liners.
2. In a bowl, whisk together the yogurt, eggs and milk until combined. Set to the side.
3. In a large bowl, combine the all-purpose flour, wheat flour, sugar, baking powder, cinnamon, baking soda and salt together. Fold the yogurt mixture into the dry mixture until combined. Gently stir in the peaches.
4. Prepare the streusel by combining the flour and brown sugar together into a small bowl. Using a fork or your fingers, cut in the butter until the mixture resembles coarse crumbs. Mix in the pecans.
5. Scoop the muffin batter into the tins, filling the large ones ¾ of the way full and the mini ones all of the way. Sprinkle the streusel topping over the muffins and place both tins in the oven.
6. Bake the mini muffins for 20 minutes and the large muffins for 25-30 or until a toothpick inserted in the center of the muffin comes out clean.
7. Let the muffins cool for 5 minutes before transferring to a wire rack to continue cooling. Store in an airtight container for up to 4 days.