Swiss and Chicken Casserole

Easy and delicious, this makes another wonderful meal for a busy night.  I usually mix everything in advance, cover and place in the fridge until it's time to bake it.  Easy-peasy!  And super tasty too!  One of my favorites!  Enjoy!
-4 cups cooked chicken, chopped into bite-size pieces
-2 cups croutons (I like to use cheese-garlic flavored, but I'm sure any other flavors work just fine)
-2 cups shredded Swiss cheese
-2/3 cups mayonnaise
-1/2 cup milk
-1 cup frozen peas (no need to thaw them)
-1/4 cup chopped onion (frozen is perfect for this)
If baking right after mixing, preheat the oven to 350 F.
In a large bowl, mix all of the ingredients together.  Make sure to mix well.  Pour into 9x13 baking dish.  You can either cover it and refrigerate until ready to bake, or pop it into the preheated oven and bake it for 40 minutes.  Enjoy!