Over medium to medium-high heat, add the oil to a large soup pot. Heat the oil for a minute or so until it’s shimmering, then add the onion, carrot, serrano, and garlic. Add salt and pepper to taste. Sauté, stirring often, until everything is softened and fragrant.
Add the harissa and stir to coat the vegetables. Cook for 3-5 minutes, until the harissa has deepened in color and there are some dark bits stuck to the pot.
Add the broth to deglaze, scraping up the dark bits to incorporate them into the broth. These bits add flavor!
Add the crushed tomato and stir. Bring to a boil and simmer for 5 minutes.
Add the pasta and white beans, stirring gently to incorporate. Simmer for about 3 minutes, or until the pasta is cooked through. This may vary depending on what pasta you’re using. Use the package instructions as a guide!
Once the pasta is cooked, add the spinach, stirring gently until wilted. Add salt and pepper to taste.
Remove from heat and add lemon juice. Serve with grated Parmesan, chopped cilantro, and lemon wedges.