Preheat oven to 375°F (190°C).
Arrange bread on a baking sheet; coat with cooking spray. Bake for 10 minutes, or until toasted, stirring halfway through.
8 ounces sourdough bread
Spray an 8-inch square baking dish with cooking spray.
In a large bowl, whisk together milk, eggs, garlic, green onion, and seasonings.
1 cup 2% milk, whole milk, or heavy cream, 1/3 cup green onions, 1 ½ teaspoons minced garlic, ½ teaspoon black pepper, ½ teaspoon grated nutmeg, ¼ teaspoon salt, 6 large eggs
In bottom of prepared baking dish, toss together toasted bread and diced ham. Pour egg mixture over top. Sprinkle with cheese.
8 ounces diced cooked ham, 1/2 cup shredded cheddar cheese
If making ahead, cover the casserole and place it in the refrigerator for at least 1 hour, or overnight.
Bake uncovered at 375°F (190°C) for 25 minutes, or until strata is puffed around the edges and a knife inserted in the center comes out clean.