Preheat the oven to 425ºF.
Combine the oats, flour, sugars, and salt in a large mixing bowl.
Stir the vanilla into the melted butter, and then pour the butter into the dry ingredients. Mix until well-combined and no streaks of dry flour are left.
Crumble and drop the mixture in nickel and quarter size pieces on top of your prepared fruit. If making a berry crisp, form the topping into flat shingles to place on top of the filling, which helps them not sink down into the center.
Bake for 45 to 60 minutes, until the topping is golden brown and the fruit filling is bubbly.