Whisk together all dressing ingredients in a medium bowl until smooth. Adjust with more lemon juice, water, or broth to achieve desired taste and consistency.
Preheat oven to 450°. Coat a baking sheet with olive oil cooking spray. Arrange asparagus spears in a single layer and season to taste with salt and pepper. Spray again with cooking spray. Roast 10–12 minutes (depending on thickness), or until tender and dark green.
Arrange roasted asparagus on a serving dish and drizzle with dressing. Serve extra dressing on the side.