Step 1

Preheat the oven to 350 degrees F (175 degrees C).

Step 2

Bring a large pot of lightly salted water to a boil. Cook elbow macaroni in the boiling water, stirring occasionally, until tender yet firm to the bite, about 8 minutes.

Step 3

While the macaroni is cooking, combine chicken, Swiss and mozzarella cheeses, mayonnaise, basil, and onion in a bowl. Add spinach, condensed soup, garlic powder, thyme, and pepper; mix to combine.

Step 4

Drain macaroni. Gently stir into the chicken mixture. Transfer to an ungreased 9x13-inch baking dish.

Step 5

Toss bread crumbs with melted butter; sprinkle over the casserole.

Step 6

Bake, uncovered, in the preheated oven until bubbly, 40 to 45 minutes.