Tex Mex Roasted Chicken Spaghetti

Name: Tex Mex Roasted Chicken Spaghetti
Ingredients: 16 ounces spaghetti; 3 tablespoons butter; 1/2 cup onion diced; 2 to 3 cloves garlic minced; 3 tablespoons all purpose flour; 1 1/2 cups chicken stock; 1 cup milk; 1/2 cup sour cream; 8 ounces grated white cheddar cheese; 1 10 oz. can diced tomatoes and green chilies, undrained; 1/2 teaspoon cumin; 1 teaspoon chili powder; Dash of cayenne pepper; Salt and pepper to taste; 2 cups cooked shredded chicken; 2 tablespoons chopped fresh cilantro; Diced tomatoes for garnish, optional