Yeah, you can train, or train out, just about anything, and having the awareness of the target is half the battle, so doing things like the suggested one-legged pedaling exercises are good, but even just practicing to put more effort into pushing with the weak leg while pedaling will both strengthen it and set up the habit of making it work. Of course, off the bike weight training will also help you achieve the muscular symmetry you're looking for.

That said, some L/R imbalance in the pedal stroke is pretty normal, and nothing to worry about necessarily.