Toast pecans over medium/low heat in a non-stick skillet, stirring frequently for 1-2 minutes until you begin to smell a nutty aroma. Set aside.
Heat olive oil in a large skillet over medium-high heat. Sauté onion, garlic, sage, thyme, rosemary, salt and pepper about 5 minutes or until onions are soft. Meanwhile, cook rigatoni according to package directions, reserving ½ cup cooking liquid before draining.
Sprinkle flour evenly onion mixture and stir to distribute. Cook for 1 minute. Stir in chicken broth and half & half. Bring to a boil. Reduce heat to medium and let simmer for about 3 to 4 minutes to thicken. Reduce heat to low and stir in pumpkin puree, Parmesan cheese and Cheddar until melted.
Add drained noodles to pumpkin sauce and stir to combine. Stir in reserved pasta water to thin sauce, if needed. Sprinkle reserved pecans over the pasta.