Cook the spaghetti in a large pot of salted boiling water according to package directions until al dente, then 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, stirring, for 1 minute until fragrant.
Add the ground beef and increase heat to medium-high. Cook, breaking up the meat, until no longer pink, about 6–8 minutes. Drain excess fat if needed.
Reduce heat to medium and stir in the taco seasoning, Rotel tomatoes (undrained), tomato paste, beef broth, and softened cream cheese. Cook, stirring occasionally, until the cream cheese melts and the sauce is smooth, about 5 minutes.
Add the cooked spaghetti to the skillet and toss to combine with the sauce. Stir in the shredded Colby Jack cheese until fully melted and the pasta is evenly coated.
Garnish with chopped fresh cilantro and serve immediately.