Start by chopping all your vegetables uniformly. I like steaming broccoli for 2–3 minutes before mixing to keep it tender yet firm. Sauté onions, garlic, and mushrooms in a little olive oil to bring out their natural sweetness.
Boil egg noodles according to package instructions, just until al dente. Drain and set aside because they’ll finish cooking in the oven without getting mushy.
In a large bowl, combine shredded chicken, sautéed vegetables, cream of mushroom soup, milk, half of the cheese, salt, pepper, and thyme. I always taste the mixture before baking to adjust seasoning.
Grease your casserole dish lightly and layer in the noodle mixture. Sprinkle breadcrumbs and remaining cheese on top for a golden, crispy finish. Make sure the topping is even so it bakes consistently.
Bake at 350°F (175°C) for 25–30 minutes until bubbly and golden on top. I usually let it rest for 5 minutes after removing from the oven to make serving easier.