Drop asparagus into a large pot of boiling water and cook until bright green and slightly softened, 1 to 2 minutes. Drain asparagus and rinse with very cold water until cool.
In a large bowl, whisk together lemon juice, mustard, oil, and herbs. Add asparagus, onion, pine nuts, feta, salt, and pepper, and stir to combine.
Note: Nutritional analysis is per serving.