To start, you'll want to use miniature ingredients — snack-size chocolate bars and mini marshmallows — so the top of the banana bread doesn't get overly crowded.
Crumble up the graham crackers or break them up into shards, and choose a relatively plain banana bread recipe so that the s'mores toppings will have a chance to shine.
For a freshly melted take, you can add everything when the banana bread is hot out of the oven, letting the chocolate and marshmallows melt together from the residual heat.
If you want a more roasted effect, add the marshmallows to the banana bread in the last 10 to 15 minutes of baking. Enjoy the s'mores-encrusted banana bread while warm.