This dish is absolutely excellent! Lovely! If you choose, use bow-tie pasta or some other small pasta. Found on a food blog and can't remember which, am sorry.
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.