Bring a large pot of salted water to a boil. Add the spaghetti and cook according to package instructions until al dente. Reserve 1 cup of pasta cooking water, then drain the pasta.
While the pasta cooks, heat the olive oil in a large skillet over medium heat.
Add the minced garlic, chopped anchovies, and red pepper flakes to the skillet. Cook, stirring frequently, until the garlic is fragrant and the anchovies have dissolved, about 2 minutes.
Add the crushed tomatoes, Kalamata olives, capers, and dried oregano to the skillet. Stir to combine and bring the sauce to a simmer.
Let the sauce simmer gently for 10 minutes, stirring occasionally, until it thickens slightly.
Season the sauce with salt and freshly ground black pepper to taste.
Add the drained spaghetti to the skillet with the sauce. Toss well to coat the pasta evenly, adding reserved pasta water a little at a time if needed to loosen the sauce.
Remove the skillet from heat and stir in the chopped parsley.
Divide the pasta among serving plates and, if desired, sprinkle with grated Parmesan cheese.
Serve immediately.