Creamy White Lasagna Soup

Name: Creamy White Lasagna Soup
Ingredients: 1 tablespoon olive oil; 1 yellow onion , diced; 2 teaspoons salt , divided, plus more to taste; 16 ounces cremini or button mushrooms , thinly sliced; 3 cloves garlic , minced; 1 quart unsalted chicken stock or broth; 2 cups water; 5 sprigs fresh thyme, or 3/4 teaspoon dried thyme; 1 bay leaf; 1 pound boneless, skinless chicken breasts or thighs; 8 ounces dry lasagna noodles; 10 ounces baby spinach; 1 cup ( 4 ounces ) freshly grated Parmesan cheese; 2 cups whole milk; Ricotta , to serve; Freshly ground black pepper , to taste