Preheat the oven to 400°F and line a baking sheet with parchment paper. Toss the banana slices with brown sugar, melted butter and cinnamon, spread them out and roast for 15 to 20 minutes until caramelized and bubbling.
Let the bananas cool for 15 minutes. Roasting deepens their flavor so the ice cream tastes just like a warm slice of banana bread. Lower the oven to 350°F. Spread the banana bread cubes and walnuts on a separate baking sheet and bake for 8 to 10 minutes until toasted and crisp on the outside, then let cool completely.
Scrape the roasted bananas and all their syrupy juices into a high-speed blender. Add the cottage cheese, milk, heavy cream, maple syrup, brown sugar, vanilla, nutmeg and salt and blend for 1 to 2 minutes until completely silky.
Pour the base into a container and refrigerate for at least 2 hours until very cold.
Churn the base in a pre-frozen ice cream maker for 20 to 25 minutes, until thick like soft serve.
Spoon one third of the ice cream into a freezer-safe container and scatter with some of the toasted banana bread cubes and walnuts. Repeat the layers, finishing with cubes and walnuts on top.
Press plastic wrap onto the surface and freeze for 3 to 4 hours until firm. Let it soften at room temperature for 10 minutes before scooping.