When I think of lean-muscle I think of low body fat percentage and strong yet compact muscle. For that I'd probably do the same that I would to lose weight in general, count calories so I'm eating at a caloric deficit while keeping macros more toward protein and fat. At the same time, I'd hit the gym a few times a week to do strength training. I don't think it's a very comfortable way to live but if your goal is to be lean and strong then it makes sense to me to eat and train that way.