Bring a large pot of water to a rolling boil and add a generous amount of salt (about 1 tablespoon). Add the spaghetti and cook according to package instructions until al dente, usually 8-10 minutes.
Reserve ½ cup of pasta cooking water before draining the pasta. This starchy water will help create a silky sauce that clings to the spaghetti.
While pasta is cooking, heat olive oil in a large skillet over medium-high heat. Add the ground beef, breaking it apart with a wooden spoon. Season with salt and pepper, and cook until browned and no longer pink, about 5-7 minutes.
Reduce heat to medium-low and add 4 tablespoons of butter to the beef. Once melted, add the minced garlic and red pepper flakes. Cook for 1-2 minutes until the garlic is fragrant but not browned (burnt garlic will taste bitter).
Add the dried oregano and stir to combine all the flavors. Cook for another 30 seconds to allow the herbs to bloom in the hot butter.
Add the drained pasta directly to the skillet with the beef and garlic butter. Toss everything together, adding the remaining 2 tablespoons of butter and the reserved pasta water a little at a time until the sauce is smooth and coats the pasta evenly.
Remove from heat and immediately add the Parmesan cheese, tossing quickly to create a creamy sauce before the cheese can clump.
Garnish with fresh parsley and additional grated Parmesan. Serve immediately while hot for the best flavor and texture.