Cook the spaghetti in a large pot of boiling salted water according to package directions until al dente, drain, and set aside.
Heat the olive oil in a large skillet over medium heat. Add the diced onion and cook until tender and translucent, about 5–6 minutes.
Add the minced garlic to the skillet and cook 1 minute more until fragrant.
Add the ground beef and cook over medium-high heat, breaking it up with a spoon, until no longer pink; drain excess fat if desired.
Reduce heat to medium and stir in the taco seasoning, Rotel tomatoes (with juices), tomato paste, beef broth, and softened cream cheese. Cook, stirring occasionally, until the cream cheese is melted and the sauce is combined, about 5 minutes.
Add the cooked spaghetti to the skillet and stir in the shredded Colby Jack cheese until fully melted and the pasta is coated with the sauce.
Garnish with chopped fresh cilantro and serve immediately.