Sauté the aromatics. In a large pot, warm olive oil and butter over medium heat.
Add onion and celery with a pinch of salt. Cook 4–5 minutes until softened. Stir in garlic and cook 30 seconds until fragrant.
Add mushrooms (optional). Toss in sliced mushrooms and cook 5–6 minutes until they release moisture and start to brown.
This adds a savory depth that mimics the heartiness of lasagna.
Build a light roux. Sprinkle flour over the vegetables and stir for 1 minute. This helps thicken the soup later without making it too heavy.
Pour in broth and season. Slowly whisk in chicken broth to avoid lumps. Add Italian seasoning, thyme, black pepper, and red pepper flakes if using.
Bring to a gentle boil.
Cook the noodles. Add broken lasagna noodles. Stir to prevent sticking. Simmer 10–12 minutes, or until the pasta is al dente.
Stir in chicken. Add shredded or diced chicken and simmer 2–3 minutes to warm through.
Taste and adjust salt.
Make it creamy. Lower the heat. Whisk in cream cheese until smooth, then add heavy cream. Avoid boiling once the dairy is in to keep it silky.
Add the cheeses. Stir in Parmesan and mozzarella until melted.
The soup should look glossy and lightly thickened.
Finish with greens and lemon. Fold in spinach until wilted, 1–2 minutes. Add lemon zest and a squeeze of lemon juice to brighten the flavors.
Garnish and serve. Ladle into bowls and top with more Parmesan, cracked pepper, and chopped parsley or basil. Serve with warm bread if you like.