If it's primarily a chocolate recipe the coffee is there to add flavour. You may be able to simply omit it. I would generally replace it with the same quantitity of (unsweetened) cocoa powder as otherwise the recipe may be a little too sweet.
If you find the overall recipe lacking in flavour after that, try more cocoa or adding a tiny bit of a compatible flavour, for a different but still good effect. One thing that works well with chocolate is vanilla, another is ginger (though too much and it will dominate - good, but not what you asked for). If the espresso powder is dissolved in liquid before adding, you can use liquid extracts to replace some of the liquid (but be careful what you buy if you also avoid alcohol as many who avoid coffee do). This gives you slightly more choice, as you can use a little almond extract, or even mint, or replace the liquid with orange juice. Of the flavours I mentioned, the almond and the vanilla would be best for just adding a subtle bit more flavour, while the others are conventionally used with chocolate in some recipes and ould go well, though change the end result.
If the recipe is a mocha recipe, or there's a lot of coffee in there, I suggest looking for a similar recipe with no or less coffee. This is always an option.