In colander or strainer rinse peas with hot water to thaw.
In saucepan mix celery, onion, bouillon granules, and 1/2 cup water.
Cover; bring to boiling.
Reduce heat and simmer till celery is tender, 12 to 15 minutes.
Stir in peas, tomato sauce, butter, and oregano.
Turn mixture into 1 1/2-quart casserole.
Bake, uncovered, at 400° till done, about 30 minutes.
Sprinkle with Parmesan cheese.