In a medium pot, bring 2 1/2 cups water to a boil. Add couscous, cover and cook 10 minutes. Drain and rinse under cold water.
Meanwhile, make pesto. In a blender or food processor, combine basil, pine nuts, garlic and lemon juice. Process, slowly streaming in oil until smooth. Remove to a large bowl and stir in Parmesan and 1/4 tsp of the salt.
Mix couscous, chicken, tomatoes, mozzarella and remaining 1/2 tsp salt into pesto. Stir well to combine.