Discard tough stems from greens. Cut top 5 inches from greens and reserve. Cut remaining greens into 3/4-inch slices. Transfer all greens to a large serving bowl. Coarsely chop nuts and finely chop garlic. In a small heavy skillet cook garlic and nuts in grapeseed oil over moderate heat, stirring, until garlic is golden. Stir in vinegar, hazelnut oil, and thyme. Season with salt and pepper, to taste.
Pour hot vinaigrette over greens and toss to combine.