Preheat the oven to 350°F (180°C).
In a large bowl, combine sliced nectarines, brown sugar, cornstarch, ground cinnamon, lemon juice, and a pinch of sea salt. Stir to combine and coat the fruit evenly. Transfer to a small baking dish* and set aside.
In a medium-size bowl, using a fork, combine rolled oats, oat flour, brown sugar, ground cinnamon, and a pinch of sea salt. Add vegan butter and mix well into a crumbly mixture.
Cover the fruit evenly with the oat crumble topping and bake in the preheated oven for about 25 minutes until golden brown on top and the nectarines are tender.
Let the crisp cool slightly before serving. Top it with vegan ice cream, dairy-free yogurt, or coconut whipped cream, and a drizzle of maple syrup.
Enjoy!