In a large bowl whisk together the eggs, milk, and dijon mustard.
Reserve a quarter of the diced red bell pepper and the green bell pepper. Set aside.
To the egg mixture stir in the bread, ham, onion, and diced peppers.
Butter or spray a 9x13 baking dish.
Pour the mixture into the dish.
Top with both types of cheese and the reserved bell peppers.
Cover with plastic wrap and place it in the fridge overnight or for up to 12 hours.
When ready to bake preheat the oven to 350 degrees.
Let the casserole sit on counter for 30 minutes to take the chill of while the oven preheats.
Bake the casserole at 350 for 55-60 minutes, you may need to cover it with foil if it begins to brown too quickly.
Remove from the oven and serve!
Top with scallions when serving if desired.
Notes
Store leftovers in the fridge for up to 5 days.
You can swap out the meat in this dish, try it with cooked sausage or bacon!
You can spice this up by adding diced jalapenos or diced green chiles.
Use whatever cheese you like, swiss would be great.
I use sandwich bread but any kind of bread would be great, croissants would work, Italian bread, brioche or you can even add more than one kind of bread - but keep in mind that some of them will absorb more of the liquid or less - so the final result could be either dryer or moister than this original recipe!