Preheat oven to 425 degrees F.
Cook onion, garlic, oregano, and red pepper flakes in 1 tablespoon oil in a 4-quart heavy pot over moderately high heat, stirring, until onion is softened, about 3 minutes. Add wine and boil until reduced by 1/2, about 3 minutes. Stir in tomatoes and salt, then reduce heat, and simmer briskly, stirring frequently, until slightly thickened, about 8 minutes. Stir shrimp into sauce and simmer, stirring occasionally, until shrimp are just cooked through, about 3 minutes.
While sauce and shrimp are cooking, cook orzo in a 6-quart pot of boiling salted water until al dente. Reserve 1/2 cup cooking water, then drain orzo in a sieve. Return orzo to pot and toss with remaining tablespoon oil. Stir in sauce with shrimp and reserved cooking water, then add olives and salt and pepper, to taste.
Spoon 1/2 of pasta into an oiled 13 by 9 by 2-inch glass baking dish, then sprinkle with 1/2 of feta. Top with remaining pasta and feta, then bake in middle of oven, uncovered, until cheese is slightly melted and pasta is heated through, 10 to 15 minutes.
Recipe courtesy of Gourmet Magazine