In a large pot over medium-high heat, add the sun-dried tomatoes and a few tablespoons of their oil. Add the chopped onion, minced garlic, and minced sage leaves and sauté until soft and fragrant, about 5-7 minutes.
Stir in the pumpkin puree, tomato puree, chicken broth, dried basil, and cinnamon. Bring to a simmer and cook for 15 minutes, adding more water or broth if needed to maintain a sauce-like consistency.
Carefully puree the sauce using an immersion blender directly in the pot until mostly smooth. Alternatively, transfer to a blender and process until smooth, then return to the pot. Stir in the cream and season to taste with salt, pepper, and red pepper flakes.
Cook pasta according to package directions until al dente. While the pasta cooks, wilt the kale in a separate skillet with a little olive oil over medium heat until tender.
Drain the pasta and toss it with the prepared pumpkin sauce. Serve immediately, topped with the sautéed kale.