Unilateral Leg Work would be a good way to fix the problem but it might not be the root of your problem. Plenty of strong, symmetrical people have built their legs without unilateral movements. Split Squats, Step ups, and Lunges do kick ass since you can increase the load you're using faster than you can with squats, and they do offer good variety, but they're not essential to building strong legs...they're just really helpful.
What's really important is that you check to see if your stance and body position is symmetrical in the big lifts. And if you do a lot of staggered starts or a lot of jerks where you always put 1 foot forward instead of the other you should correct your poor symmetry and start doing your split jerks with alternating split stances.