Prepare Hazelnut Vinaigrette. Set aside. (Vinaigrette can be made a day ahead. Whisk before using.)
Separate leaves from each head of lettuce. Each individual salad requires 5 leaves, ranging in size from about 4 inches in diameter to 1-1/2 inches in diameter.
To compose salad, on each of 4 individual plates, layer the largest leaf (about 4 inches), a few chopped tomatoes, a few red onion slivers, a sprinkling of nuts, and a drizzle of Hazelnut Vinaigrette. Repeat layering, stacking carefully, until all of the lettuce leaves are used. Top each serving with finely shredded manchego or Parmesan cheese. Makes 4 salads.
In a small bowl whisk together champagne vinegar or white wine vinegar, shallots, salt, and pepper. Slowly whisk in hazelnut oil.