Bring a large pot of salted water to a boil. Add 1 cup orzo and cook according to package directions, adding peas during the last 5 minutes of cooking. Drain and toss with lemon juice, olive oil, and 1/4 tsp. salt. Cover to keep warm and set aside.
In the same pot add 2 inches of water. Bring to boiling; reduce heat to a gentle simmer. Add cod to the simmering water and cook 2 minutes; remove with a slotted spoon.
Meanwhile, in a small bowl mix lemon zest, chives and melted butter. Serve cod over orzo with the butter sauce spooned on top.
If frozen, place the cod in the refrigerator the night before to defrost.