Heat oven to 350°F/175°C. Lightly grease a 7- to 9-inch/18- to 23-centimeter pie dish or baking dish.
Place chopped strawberries in a medium saucepan over high heat. When they reach a boil, reduce to medium and mash gently as they soften. Cook, stirring, about 10 minutes, leaving some small chunks for texture.
Stir in lemon juice and maple syrup and cook 5 minutes longer. Mix in vanilla extract and chia seeds, then simmer for 5 minutes, until thickened. Scrape the filling into the prepared baking dish.
In a medium bowl, combine oats, oat flour, coconut oil, maple syrup, vanilla, and salt. Mix with a fork until a sticky crumble forms, then scatter evenly over the strawberry filling.
Bake for 25 to 30 minutes, until the topping is golden and the filling is bubbling. Serve warm, or cool 20 minutes before adding ice cream.