1. Bring stock to a simmer in a saucepan (do not boil). Keep warm.
2. Heat a saucepan over medium-low heat. Add butter and oil; swirl to coat. Add scallions; cook 7 minutes, stirring occasionally. Add orzo; cook 2 minutes, stirring frequently. Stir in rind, juice, salt, and pepper. Add 1/2 cup stock to pasta mixture; cook 2 1/2 minutes or until liquid is nearly absorbed, stirring frequently. Reserve 1 cup stock. Add remaining stock, 1/2 cup at a time, stirring frequently until each portion of stock is absorbed before adding the next (about 13 minutes). Stir in remaining 1 cup stock and asparagus; cook 7 minutes or until asparagus is tender, stirring occasionally. Remove from heat; stir in half of cheese. Sprinkle with remaining cheese and parsley. Serve immediately.