Prep your pan and oven. Heat the oven to 350°F (175°C). Line a 12-cup mini muffin pan or a 24-cup mini pan depending on size, or lightly grease a standard muffin pan. For under 100 calories, aim for 12 standard muffins at about 95–100 calories each, or 24 minis at about 50 each.

Hydrate the oats. In a bowl, stir 1 cup rolled oats with 1/2 cup plain nonfat Greek yogurt and 1/2 cup unsweetened applesauce. Let it sit for 10 minutes. This softens the oats and improves texture.

Whisk the dry mix. In another bowl, combine 1/2 cup whole wheat flour, 1 teaspoon baking powder, 1/4 teaspoon baking soda, 1/4 teaspoon fine salt, and 1/2 teaspoon ground cinnamon. If you like brightness, add 1/2 teaspoon lemon zest.

Finish the wet mix. To the hydrated oats, add 1 tablespoon neutral oil, 1 large egg white (or 1 small egg), 1 teaspoon vanilla extract, and 3 tablespoons honey or maple syrup. Whisk until smooth.

Fold in the peaches. Gently stir in 1 cup finely diced ripe peaches (pat dry if using thawed frozen). The smaller the dice, the more evenly the fruit distributes.

Combine wet and dry. Add the dry ingredients to the wet and fold until just combined. Do not overmix; a few streaks of flour are fine. The batter should be thick but scoopable.

Portion the batter. Divide evenly among the muffin cups, filling each about 3/4 full. Sprinkle a few oat flakes on top if you like a toasty look.

Bake. For standard muffins, bake 14–17 minutes; for mini muffins, bake 9–12 minutes. They’re done when a toothpick comes out with a few moist crumbs and the tops spring back.

Cool properly. Let muffins rest in the pan for 5 minutes, then transfer to a rack. Cooling sets the crumb and keeps them from collapsing.

Calculate to confirm calories. With the listed amounts and 12 standard muffins, each should land under 100 calories. If you add extra sweetener or larger peach chunks, recheck your portions.