I don't think that washing will be enough to remove all traces of pesticides. I assume that some of the pesticides are embedded in the peel by the time the fruit is harvested. But don't take my word for it.
It might be better to just pick untreated fruit from the beginning, if possible.
a dozen banana peels, washed and scrubbed, cut into large chunks (frozen peels are OK)
½ litre of water
800g of sugar
juice of a whole lime
random amount of cloves and cinnamon
Cook the banana peels in the water, stirring occasionally, for five minutes or so.
Blend the mix.
Cook the blend again, alongside the other ingredients, stirring occasionally, for 40 additional minutes. It should thicken quite a bit, to the point that it detaches itself from the bottom of the pot. Let it cool and it's done.
You could also cover them in syrup and fry them, but that requires a lot of peels, and unlike the recipe above you can't freeze the peels, it gets a weird texture.
It sounds like a lot but it's roughly the same weight in banana peels and sugar, it's typical for this sort of jam. For reference: you could sub the peels for the same weight in strawberries, and the recipe still works.
EDIT: it is by no means something healthy to eat in large quantities. It's a caloric bomb, just like any jam. But it works great as a bread spread, the banana peels won't go to waste, and it packs a lot of potassium too. (Most potassium from bananas is in the peel, not in the flesh.)
I also have a banana cake recipe if anyone is interested. It uses the whole banana but you can tweak it to use just the peels.