Preheat the oven to 375F / 190c.
Slice the mushrooms, onion and garlic.
8 ounces white mushrooms, 1 onion, 3 large cloves garlic
Heat the oil in a skillet on a medium high heat. Once hot, add the sliced veggies and a little salt and pepper. Sautee til browned.
1 teaspoon oil, pinch salt and black pepper
Add all of the ingredients, along with the sauteed vegetables, to a large casserole dish. Use just half of the parmesan.
5 ounces baby spinach, 17 to 18 ounces orzo pasta, 1 pound cooked chicken, 1 cup heavy cream (35%), 3 cups chicken stock or broth, juice of 1 lemon, 1 cup mascarpone cheese, 1 cup shredded or flaked parmesan cheese (divided in half), 1 teaspoon salt, ½ teaspoon black pepper, 1 tablespoon dried oregano
Stir everything together until well combined.
Sprinkle on the remaining parmesan.
Bake uncovered in the preheated oven at 375F / 190c for 40 to 45 minutes, until the orzo pasta is soft.
Let stand for 10 minutes before serving.