Shred the lettuce leaves and put them in a large shallow dish or individual serving dishes. Sprinkle the spring onions over the lettuce.
Cut the capsicum quarters across into thin strips and arrange them in the dish. Halve, stone and peel the avocado, and cut into 5 mm slices across the width. Peel, halve and deseed the papaya, and cut into 5 mm slices across the width. Scatter the avocado and papaya slices over the capsicum strips.
Whisk all the dressing ingredients together and pour over the salad. Heat a small heavy saucepan, add the pepitas and toss them in the pan for a few minutes to toast them lightly. Sprinkle the pepitas over the salad, then serve.