In a large bowl, stir together the basil pesto, mayonnaise, and fresh lemon juice until the dressing is smooth and evenly combined.
Season with salt and black pepper. Stir once more.
Add the diced cooked chicken breast to the bowl. Toss until every piece of chicken is fully coated in the pesto dressing.
Gently fold in the fresh mozzarella pearls and quartered cherry tomatoes. Be careful not to crush the mozzarella or tomatoes as you mix.
Scatter the toasted pine nuts and sliced fresh basil over the top and fold them through the salad one final time.
Serve right away at room temperature for the best flavor, or cover and refrigerate for up to a few hours. This salad is perfect scooped onto crusty Italian bread, in a wrap, or served alongside a simple green salad.