Preheat oven to 350.Combine squash, ½ tablespoon oil, sage, garlic, ½ teaspoon salt, and black pepper in a large bowl; toss to coat. Arrange squash mixture on a baking sheet coated with cooking spray. Bake at 425° for 30 minutes or until squash is tender. While squash is roasting, cook pasta according to package directions. Drain and return to stock pot.

Heat remaining oil in a large Dutch oven over medium-high heat. Add onion, and sauté for 4 minutes. Reduce heat to medium-low; continue cooking for 20 minutes or until golden brown, stirring frequently. Place onion in a bowl.

Heat 2 ½ cups milk, and thyme in a medium saucepan over medium-high heat. Bring to a boil; remove from heat. Let stand for 10 minutes. Discard thyme. Return pan to medium heat. Combine remaining ½ cup milk and flour in a small bowl. Add to pan, stirring with a whisk until blended. Bring to a boil; reduce heat, and simmer for 5 minutes or until thickened, stirring constantly. Remove from heat; stir in teaspoon salt, cheese, and nutmeg.

Add spinach and hot sausage to cooked pasta. Pour cheese sauce over top of pasta mixture and stir to coat.

Place pasta in a large casserole and sprinkle with Italian Seasoned Breadcrumbs. Bake for 30-40 minutes or until hot and bubbly.