Light and dark greens, the mildly acid fruit, and the creamy avocado provide a lively dynamic in this simple salad.

Steps

1. Separate the leaves of the lettuce and remove the spinach stems. Discard any leaves that are bruised or yellow, wash the greens (wash the spinach in two changes of water), and dry them in a spinner.
2. If the spinach leaves are small, leave them whole. If they are large, layer several leaves together, roll them up, and slice them into wide or narrow ribbons. Place them loosely in a kitchen towel and refrigerate until needed.
3. Use a very sharp knife to peel the grapefruit. Slice a piece off the top and the bottom of each, then work down the sides, removing the white pith as well as the peel. Holding the grapefruit over a bowl to catch the juice, cut each section loose from its membrane and turn it into the bowl. (Later you can drink the juice.)
4. Peel the avocadoes, slice them in half, and remove the seeds. Lay the halves cut sides down and slice them crosswise at an angle.
5. Combine the vinegars, shallot, and salt in a bowl. Whisk in the oil. Taste, and adjust the balance of vinegar and oil if necessary. Stir in the mint and chives.
6. Pour the juice off the grapefruit sections, combine the grapefruit with the avocado slices, and dress them both carefully with some of the vinaigrette. Toss the greens with the rest of the vinaigrette and lay them on salad plates. Set the grapefruit and avocado slices in and among the leaves. Add a grinding of black pepper (or roasted Szechuan pepper) and serve.