Peel and stone the avocados. Slice thinly, then add to the bowl and toss to cover in the lemon juice. Once the quinoa is dry, transfer it to the bowl. Add the broad beans, garlic, radishes, cumin, olive oil and chili flakes and some salt and pepper. Toss very gently, without breaking the avocado. Taste and add more salt and pepper, if you wish. Plate and garnish with watercress.