Heat a Dutch oven or large pot over medium-high heat and brown the ground beef with the chopped onion until the beef is fully browned and the onion is softened, about 5–7 minutes. Drain excess fat if desired.
Add the garlic and cook, stirring, for about 1 minute until fragrant.
Stir in the Rotel tomatoes, tomato sauce, taco seasoning, beef broth, tomato paste, and Worcestershire sauce. Bring the mixture to a boil.
Add the spaghetti noodles, reduce heat to medium so the mixture simmers, and cook uncovered, stirring frequently and scraping the bottom of the pot, until the noodles are tender, about 15–18 minutes.
With about 5 minutes remaining, stir in the shredded cheddar and Monterey Jack cheeses until melted and evenly combined.
Remove from heat, garnish with chopped cilantro if desired, and serve immediately.