Grease a 9-by-13-inch baking dish with butter or cooking spray.
In a large skillet, heat the olive oil. Add the sausage and brown over medium heat, breaking up pieces with spoon and until the fat is rendered, about 3 minutes. Add the red onion and cook until lightly browned and tender, about 5 minutes. Add the bell peppers, kosher salt, pepper and cook, about 7 minutes. Let cool completely.
In a bowl, whisk together the eggs, cream, water and maple syrup. To the greased baking dish layer the bread, vegetable mixture, ham, green onion and cheese. Pour the egg mixture evenly over all and cover with plastic wrap. Refrigerate overnight to set.
Preheat oven to 350°F. Uncover the casserole and bake for about 50 minutes, until it’s just set and the top is browned. Let stand for 10 minutes before serving.