(Get your pasta cooking if it’s not already cooked!)
In a large pot, warm the oil over medium heat. Add the leeks, carrots, celery and ½ teaspoon salt and cook until softened, about 5 minutes. Add the garlic, rosemary or sage, fennel seeds, and red pepper flakes (if using) and cook for 30 more seconds, stirring constantly.
Add the tomato paste and stir to coat the vegetables and spices. Cook for 2 more minutes, stirring often, to caramelize the tomato paste.
Stir in the squash and mushrooms to coat in the tomato paste. Stir in the water, beans, and remaining 1 ½ teaspoons salt. Bring to a boil, give it a stir, then reduce heat to low and simmer, covered, for 15 minutes, or until the squash is tender.
Remove from heat and stir in the kale until wilted. Taste and add more salt, if needed (I usually add an extra hefty pinch at the end). Add pasta to your bowl and ladle the soup over top. Drizzle with olive oil and sprinkled with shredded parmesan (if using) and black pepper.