Place parchment on baking tray that will fit in your freezer.
Slice the bananas and arrange them on parchment. Place a second piece of parchment on top. Use a flat bottomed ramekin to press bananas down.
Top with runny tahini. Use an offset spatula to spread tahini evenly.
Scatter the mixed nuts on top.
Melt chocolate and oil in 30 second increments in the microwave until smooth and silky. Pour over the nuts. Use a spatula to spread as evenly as possible.
Sprinkle with sesame seeds and pop it in the freezer for 20 minutes.
Remove from freezer and top with flaky salt. Place back in the freezer overnight.
Use a sharp knife to cut into pieces. Store in freezer in an airtight container.