Combine the peaches, sugar, flour, lemon juice, vanilla, and salt in a large mixing bowl. Gently toss until peaches are evenly coated. Spread the filling in the bottom of the prepared baking dish. Set aside.
Combine the flour, brown sugar, cinnamon, and salt in a mixing bowl. Combine. Add the oats and cubed butter to the mixture and then cut the butter into the dry ingredients using a pastry cutter or a fork. Sprinkle the topping evenly over the filling.