Well this is my way, and actually lean muscled legs wasn't my goal at all. I eat a lot of pasta, rice, bread combined with meat and vegetables. But yea, pasta is the most important, because it helps to burn fat faster as you work out.

It is also the type of riding you do. You should concentrate on maintaining the same pace all the time. First you may think that riding is easy, but wait, keep the same tempo for 30 - 45 minutes and even longer if you can. You will feel the pain and eventually riding will become very hard. Do this exercise every day and in about one month you'll see the result.

Also you can go to gym, your goal is endurance, light weight and 30 -40 repetitions.