Wash and slice the tomatoes. Peel the mango, cut the flesh from the stone and slice. Season the tomato and mango with salt and pepper, and leave to stand for 10 minutes.
Meanwhile, wash the lettuce, shake dry and cut into small pieces. Wash the spring onions and cut into rings. Mix the lettuce and spring onions with the tomatoes and mango.
Wash the basil, shake dry and finely chop the leaves. Mix the basil with balsamic vinegar and olive oil and season with salt and pepper. Pour the dressing over the salad.
Drain the mozzarella, tear into pieces and scatter over the salad.