Preheat the oven to 350 degrees F (175 degrees C). Lightly grease two 8-ounce ramekins and place them on a baking sheet.
Make the filling: Combine apples, maple syrup, lemon juice, vanilla extract, cinnamon, nutmeg, allspice, and salt in a bowl; toss until thoroughly mixed. Divide mixture between the prepared ramekins.
Prepare the topping: Combine oats, flour, maple syrup, cinnamon, and salt in a bowl; mix until thoroughly combined. Cut in softened butter until mixture resembles coarse crumbs. Sprinkle crumb topping evenly on top of the filling in the ramekins.
Place baking sheet with ramekins into the preheated oven and bake until apples are tender and the topping is slightly browned, 25 to 30 minutes. Cool for 10 to 15 minutes before serving.