This chocolate babka french toast with caramelized banana creme anglaise will satisfy all of your chocolate and banana cravings (and probably more).
I've only had the Trader Joe's chocolate babka (found near all their tarts and baked goods), and can't comment on how other ones would taste in this. The TJ's version is pretty chocolatey and sweet, so you may need to adjust the amount of cocoa/sugar in the French toast custard/dip to account for variances between your babka and the TJ's one.
If you're having trouble tracking down chocolate babka, try Trader Joe's and Albertson's. However, you don't need to use chocolate babka. Challah works fine, though it won't be as rich. If you use a bread that doesn't have chocolate baked into it, I'd suggest adding 3-4 T granulated sugar and increasing the cocoa by 1-2 T (for 3-4 T total) for the custard, depending on taste. You may need more custard/dip for the bread, depending on how thick your slices are, how long you let them soak, etc. I'd also recommend adding chopped dark chocolate on top of the hot French toast so that you still get the melty/gooey chocolate factor.
If you're lazy and reallllyyyy don't care about your caloric intake, stir the caramelized banana puree into some melted vanilla ice cream and forgo making the custard. It's hardcore dessert and not breakfast at this point.