Add the ground beef to a soup pot/Dutch oven over medium-high heat, and cook until just browned, breaking it up with your spoon as you go along (about 7-8 minutes). Spoon out excess fat if needed.
Stir in the tomato paste and garlic, and cook for about a minute.
Stir in the onion powder, sugar, oregano, Italian seasoning, salt, and crushed red pepper flakes.
Add the beef broth and crushed tomatoes to the pot, and increase the heat to high.
Once boiling, add in the spaghetti and cook for 12 minutes, uncovered, stirring occasionally. You will need to turn the heat down at some point to maintain a constant simmer (medium or even medium-low) so it's bubbling steadily but not furiously boiling. See notes below for troubleshooting tips.
Turn the burner off (leave the pot on it). Sprinkle the mozzarella over top and close the lid for 5 minutes or until the cheese melts and more of the liquid absorbs. This recipe has lots of sauce.
Gently toss it so the mozzarella is incorporated, and season with pepper and some extra salt if needed. Serve immediately with freshly grated parm if desired.