Heat a large saucepan over medium heat and add the oil. When hot, add the meat and cook, without stirring, until browned, 3 to 5 minutes. Break it up with a wooden spoon, then add the onion and garlic and cook, stirring, until starting to soften, about 2 minutes.
Add the tomato paste and cook for 2 to 3 minutes. Add the oregano and red pepper flakes and cook for 1 minute.
Add the water, broth or dry red wine and bring to a simmer. Cook until the liquid has reduced by half, about 10 minutes.
Add the crushed tomatoes and bring to a simmer. Cook until the sauce has thickened, about 20 minutes.
Meanwhile, bring a large pot of salted water to a boil. Add the spaghetti and cook until al dente, about 8 minutes. Reserve 1 cup of the pasta cooking water, then drain the spaghetti.
Add the spaghetti to the sauce and toss to coat. If the sauce is too thick, add some of the reserved pasta cooking water to thin it out. Serve hot with grated Parmesan cheese, if desired