Preheat the oven to 400°F and grease a 10-inch cast-iron skillet.
In a large bowl, combine the peaches, cornstarch, sugar, lemon juice, and vanilla and toss to coat.
Make the topping: In a medium bowl, combine the oats, almond flour, brown sugar, walnuts, cinnamon, and salt. Using your hands, work in the firm coconut oil until the mixture is crumbly.
Scoop the peach filling into the prepared skillet. Sprinkle with the topping and bake for 20 to 30 minutes, or until the fruit is soft and the topping is golden brown.
Remove from the oven and let cool for 5 minutes. Serve with vanilla ice cream.