Stir the cornstarch and 1/4 cup stock in a small bowl until the mixture is smooth.
Heat the remaining stock, garlic powder, broccoli, carrots, pepper and onion in a 3-quart saucepan over medium heat to a boil. Reduce the heat to low. Cover and cook for 5 minutes or until the vegetables are tender-crisp.
Stir in the cornstarch mixture. Cook and stir until the mixture boils and thickens. Stir in the turkey and cook until the mixture is hot and bubbling. Toss with the spaghetti and cheese.
Tip: To save time, you can use 2 cans (4.5 ounces each) Swanson® Premium White Chunk Chicken Breast in Water, drained, for the turkey in this recipe.