This is such a fast and easy recipe I usually make for a brunch or a weekend breakfast treat. It tastes great, couldn't be quicker to make, and is a good way to take a boxed muffin mix and "kick it up a notch."
Preheat oven to 400 degrees. Grease 8-inch square or 9-inch round pan.
Drain peaches, reserving juice. Add water to reserved juice to equal 3/4 cup liquid. Chop peaches.
Combine muffin mix, egg and 3/4 cup peach liquid in medium bowl; fold in peaches. Pour batter into pan. Knead swirl packet 10 seconds before opening. Squeeze contents on top of batter and swirl with knife. Sprinkle topping over batter.
Bake for 28-33 minutes for 8-in square pan (or 20-25 minutes for 9-inch round pan), or until coffee cake is golden. Serve warm.