Bring a large pot of water to a boil. Add the spaghetti and cook according to package directions; drain, reserving 1 cup of the pasta water. Toss the spaghetti with some oil and set aside.
Add the oil, garlic, 3/4 teaspoon salt and crushed red pepper to a large skillet over medium-high heat. Once the oil begins to shimmer, add the tomatoes, reserved pasta water and oregano; bring to a high simmer and cook until the sauce thickens but is still loose, 12 to 15 minutes.
Add the fish and olives and cook, stirring occasionally, until the fish is cooked through and flaky, 3 to 4 minutes. Add the spaghetti and parsley. Toss to combine and divide among four bowls.
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