This exercise is great because it works so many different muscle groups and it can be progressive. To start, you can perform just a lunge. To make this more challenging, perform a lunge using ExcelCord.
For the lunge & twist, perform a straight lunge and as your land on your front foot, twist your shoulders and torso 45° in that direction. Once you can comfortably perform a lunge and twist, add a medicine ball and gradually increase the weight of the ball to make it more challenging. Perform two sets of eight reps on each leg.