Peel the peaches (optional step). Bring a large saucepan of water to a boil. Place 3-4 peaches in the pan at a time (or however many can be completely submerged at once) and boil for 45 seconds. Use tongs to carefully transfer the hot peaches immediately to a bowl of ice water and let them rest for at least 1 minute. Use a paring knife to slice open the skin, then peel it off with your fingers. Repeat with the remaining peaches, then remove their pits and cut them into slices.

Prep oven and baking dish. Heat oven to 350°F. Lightly mist a 9 x 13-inch baking dish with cooking spray.

Mix the filling. In a large mixing bowl, gently toss together the filling ingredients until evenly combined. Transfer the filling to the baking dish and spread it out in an even layer.

Mix the oatmeal crisp. Briefly rinse out the mixing bowl. Add the oatmeal crisp ingredients and gently toss until evenly combined. Sprinkle the oatmeal crisp evenly over the peach filling.

Bake. Bake the oatmeal crisp uncovered for about 40 to 45 minutes, or until the filling is bubbling all around the edges and the crisp is lightly browned. (If you notice midway through baking that the crisp is browning too much, gently lay a piece of aluminum foil on top of the crisp to prevent it from browning more.)

Cool. Transfer the baking dish to a wire rack and let the crisp cool for at least 5 minutes.

Serve. Serve warm with vanilla ice cream and enjoy!