Spring Pasta Salad with Asparagus

asparagus stems, peeled if tough, and ends trimmed 4 cups penne pasta 1 cup mozzarella cheese, cut into small cubes 1 large bunch (around 12) spring onions, sliced into thin rounds 24 ripe cherry tomatoes, cut in half and drained for 20 minutes in a colander to remove excess liquid 4 tbsp extra-virgin olive oil zest and juice of 1 lemon 2 tbsp toasted pine nuts 1 large handful fresh basil leaves, lightly chopped salt and freshly ground black pepper