Lightly oil a 9x13-inch baking dish and set bread cubes inside, set aside.

Add olive oil to a large sauté pan and set over medium heat. Add onion and ½ teaspoon salt and cook for 5 minutes. Add mushrooms and ½ teaspoon of pepper and cook for an additional 5 minutes. Add kale and Italian seasoning, and cook for 2 minutes, or until slightly wilted. Add vegetable mixture to the prepared pan with the bread and stir to gently distribute.

In a large bowl, whisk together eggs, milk, and remaining salt and pepper until well-blended. Add 1 cup cheddar cheese and stir to combine.

Pour the egg mixture over the bread and vegetables and sprinkle the remaining cheddar cheese, then cover tightly with foil. Let sit in the fridge overnight.

When ready to bake, preheat the oven to 350˚F. Bake, tightly covered in foil, for 40 minutes. Uncover and bake for an additional 15 minutes, or until the center is puffy and the top is golden brown.

Let cool slightly before cutting into squares and serving.