Stir the banana slices, maple syrup, and lemon juice together in a skillet. Cook over medium heat for 3 to 4 minutes, until softened and lightly caramelized, then cool completely.
Whisk the mashed bananas, coconut cream, oat milk, sugar, maple syrup, cornstarch, and sea salt in a saucepan until smooth.
Cook the banana base over medium heat for 5 to 7 minutes, whisking constantly, until slightly thickened. Stir in the vanilla extract.
Refrigerate the base and caramelized banana mixture separately for at least 4 hours.
Combine the dairy free cookie crumbs, melted butter, and sugar. Bake at 350 F for 8 minutes, then cool completely.
Churn the cold banana ice cream base in an ice cream maker until thick and creamy.
Layer the ice cream with the cookie crumble and caramelized banana pieces in a freezer-safe container, cover with parchment paper, and freeze for 4 hours.