Prepare pasta according to package directions, adding 1/2 tsp. salt to water; drain well.
Place pasta in a large bowl, and stir in tomatoes, olives, and onion.
Whisk together olive oil, next 3 ingredients, and remaining 1/4 tsp. salt; add to pasta mixture, tossing to coat. Let stand 10 minutes; stir in feta. Garnish, if desired.
Kitchen Express: Substitute 6 Tbsp. balsamic vinaigrette for olive oil, vinegar, garlic, and oregano. Proceed as directed.
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