Heat olive oil in a large Dutch oven over medium heat. Add onion, carrots, and celery and cook 6–8 minutes until softened. Add garlic, mushrooms, and bell pepper and cook 3–4 minutes until fragrant and starting to brown. Stir in oregano, basil, red pepper flakes, salt, and pepper.

Add crushed tomatoes and vegetable broth, scraping up any browned bits. Bring to a gentle simmer and taste for seasoning.

Stir in broken lasagna noodles and simmer until al dente, about 8–10 minutes. Add spinach in the last minute and let it wilt into the soup.

Reduce heat to low and stir in half the mozzarella and most of the Parmesan until melted. Ladle into bowls and top each serving with a spoonful of ricotta and torn basil. Add remaining mozzarella and Parmesan as desired.