Line an 8-by-4-inch loaf pan with plastic wrap (you can use a 9-by-5 pan if that’s what you’ve got), leaving an overhang on all sides.
Place the bananas in your food processor and process till crumbly. Scrape down the sides and continue processing the bananas will become smooth, and then thick and creamy with a consistency similar to soft-serve ice cream.
Meanwhile whisk the tahini and maple syrup till smooth to taste and adjust sweetener if needed.
Spread half the ice cream into your loaf pan and smooth with the back of a spoon. Drizzle half the tahini mixture over. Repeat with remaining ice cream and tahini. Use a thin sharp knife to swirl the mixture together; rap the pan on the counter to level.