Preheat oven to 350. Cook pasta according to package directions (usually 14-15 minutes, but don't overcook). Drain and rinse in cold water, drain again.

Meanwhile, in a large skillet, brown onion with the turkey until
the meat is cooked through. Stir in chili powder, cream cheese, and 1/2 c. taco sauce until blended. Stir in 1/2 c. shredded cheese.

Spoon about 2 Tbsp of the filling into each shell. Place shells in an 11 x 7" baking dish coated with cooking spray. Top with remaining taco sauce and cover.

Bake until heated through, 20-25 minutes. Sprinkle with remaining cheese, and bake uncovered until cheese is melted, 5-10 minutes. Serve with garnish as suggested above.