Heat the olive oil in a large stock pot over medium heat. 

Add the red pepper flakes and oregano and cook for 30-45 seconds, stirring occasionally, until just fragrant. 

Add in the onion and cook for 3-4 minutes until softened, but not browned. Stir in the garlic, olives and capers and cook another 1-2 minutes. 

Add each tomato, crushing it with your hands before adding it to the pot. Add the remaining puree and stir together, breaking up the tomatoes again in the pot with a wooden spoon. Simmer for 5 minutes. 

Add in 2 1/2 cups water and the spaghetti. If you keep the spaghetti whole, you will have to let the noodles soften, then gently flip them over and let them soften on the other side before they will submerge into the pot. Or, you can break the noodles in 1/2 and add to the pot. 

Bring the pasta to a boil over medium-high heat and cook until just al dente, stirring often. The sauce should thicken as it cooks, coating the pasta. If you need a little more water to thin the sauce, add 2 tablespoons at a time. 

Add the butter and stir together for a glossy sauce. Taste for salt; I didn't add much since the olives and capers bring in so much brine, but you might want more. Add in the parsley and parmesan cheese, if using. Serve immediately.