Preheat oven to 325°. Pulse Puffins, flour, salt, and ¼ cup granulated sugar in a food processor until ground. Transfer to a medium bowl and add melted butter; mix until a few large clumps form. Spread out crumble on a rimmed baking sheet and bake until golden for 12–15 minutes. Let cool.
Meanwhile, toss peaches, brown sugar, and 1 Tbsp. lemon juice in a medium bowl. Heat remaining 2 Tbsp. butter in a large skillet over medium; cook peaches, tossing often, until sugar is dissolved and peaches are soft, about 5 minutes. Let cool slightly.
Divide warm peaches in mason jars and layer with Greek yogurt, Puffins crumble and a few pieces of Puffins cereal.Peach Puffins