Dice the yellow onion and add to a large bowl. Thinly slice the mushrooms and add to the same bowl. Mince the garlic and add to the bowl.

Grate the Parmesan cheese and place it in a medium bowl. Grate the mozzarella cheese or measure out shredded cheese and add to the bowl.

Melt the butter in a large Dutch oven over medium heat. Add the onion mixture, 1 teaspoon kosher salt, Italian seasoning, and black pepper. Cook until onions are translucent and mushrooms begin to brown, about 12 to 14 minutes.

Season the chicken breasts with 1/2 teaspoon of kosher salt. Add to the pot.

Sprinkle flour into the pot, stirring constantly for 30 seconds to 1 minute. Slowly pour in chicken broth and water, stirring to combine.

Cook until the chicken is cooked through, about 10 to 12 minutes. Transfer the chicken to a board and shred with forks.

Break lasagna noodles into pieces and add to the soup, simmering until al dente, about 10 to 14 minutes.

Return the shredded chicken to the pot, adding spinach, heavy cream, Parmesan, and mozzarella. Cook until spinach wilts and cheeses melt, about 1 minute. Taste and adjust seasoning as needed. Ladle into bowls, dolloping with ricotta.