Prepare spaghetti per packet directions. Drain and hold.
Meanwhile, heat oil in a large skillet. Add diced chicken and sauté over medium-high heat. Chicken is done when punctured with a fork and juices run clear. Internal temperature must reach 165°F.
Add the salsa, tomato sauce and taco seasoning to the skillet. Stir to mix and bring back to a low boil.
Toss the spaghetti in the sauce to heat through. Garnish each serving with shredded cheese and sour cream.