Preheat the oven to 350°F and grease a 9x9-inch baking dish.

In a large bowl, toss the peaches with the flour, sugar, lemon juice, and vanilla. Spread evenly in the prepared baking dish.

Make the topping: In a medium bowl, whisk together the oats, flour, brown sugar, cinnamon, and salt. Use a fork, a pastry cutter, or your hands to work in the butter until the mixture is crumbly. Sprinkle evenly over the peaches.

Bake for 30 to 40 minutes, or until the peaches are bubbling and the topping is golden brown and crisp.

Let stand for 10 minutes before serving with vanilla ice cream.