Make the dressing
Combine the lemon juice, zest, thyme, garlic, and sugar in a blender or food processor; blend until smooth. With the machine running, add the oil in a slow, steady stream. Season with salt and pepper.
Prepare the salad
Heat the grill. Toss the asparagus and mushrooms with the oil and sprinkle with salt. Put the mushrooms on a medium-high part of the grill; turn them occasionally to prevent sticking. After about 10 minutes, add the asparagus and grill it, rolling frequently to avoid burning. Grill the mushrooms until dark and meaty-looking, about 15 minutes total; they should be crisp at the edges but still juicy. Cook the asparagus until browned and crisp-tender, 5 to 7 minutes, depending on thickness. Line four salad plates with the greens. Slice the mushrooms and arrange them and the asparagus on the greens. Drizzle with the dressing and serve.
nutrition information (per serving):
Photo: Mark Thomas