If a recipe calls for pecans, chopped and toasted, should I chop and then toast OR toast and then chop (or does it not so much make a difference!)?

I am with the rest of the responders in that I toast and then chop. The only addition I make is that I make sure to cool the nuts as they crisp up and chop better, in my opinion.
I also always set a timer when I toast nuts as I have a bad habit of walking away and forgetting about them and they do burn easily!

I always toast and then chop nuts. But it is possible to do it either way. As tranquility suggested, the smaller pieces are more likely to burn.

I'd say toast and then chop. It's so easy to burn small pieces of pecans (and any other type of nut).