Cook the orzo according to package directions and drain, reserving 1/4 cup of cooking liquid.
While the orzo cooks, heat the oil in a skillet over medium-high heat. Sauté the onion for a few minutes. Add the asparagus and sauté another 3 minutes or until asparagus is just tender. Remove from the heat and add the reserved cooking liquid, parsley, mint, garlic, lemon zest and juice and red pepper flakes. Mix together with the hot orzo. Season with salt and pepper and garnish the individual servings with Parmesan. Serve warm.
Add 2 tablespoons of sliced olives or oil-cured sundried tomatoes for a more complex flavor. Or skip the orzo, and serve the asparagus gremolata over couscous or quinoa with lemon wedges.