Bring a large pot of water to boil. Cook pasta according to the package directions. Drain, reserving ½ cup of pasta water. Set aside.

Meanwhile, in a large skillet or sauté pan, cook the ground meat over medium-high heat until no longer pink. A few minutes before the meat is cooked through, add the chopped onion to the skillet. Once the meat is cooked through, mix in the garlic and cook until fragrant, about 30 seconds. Mix in the diced tomatoes and taco seasoning and let simmer over medium heat for about 5 minutes. Stir in the cooked pasta, cream cheese, sour cream and reserved pasta water, and continue stirring until the cream cheese is melted and the sauce is well blended. Season with salt and pepper to taste. Simmer over medium-low heat 3-5 minutes to reduce the sauce a bit.