Butter or nonstick cooking spray, for the baking dish
1 small onion, chopped
1 pound white button mushrooms, sliced
One 8-ounce package frozen green beans, thawed
2 cloves garlic, minced
1/2 pound dried-out bread slices, cut into large bite-sized chunks, or unseasoned stuffing croutons
1 cup light cream or half-and-half
1 cup whole milk
1/4 teaspoon ground nutmeg
Kosher salt and freshly ground black pepper
1 cup canned French-fried onions
1 cup green bean chips or snap pea crisps
Preheat the oven to 350 degrees F. Butter a 13-by-9-inch baking dish or a 2-quart casserole with butter or coat it with cooking spray.
In a skillet over medium heat, cook the onions, stirring occasionally, until golden, about 3 minutes, then add the mushrooms. Continue to cook until softened, then add the green beans and garlic and cook until fragrant, 2 to 3 minutes.
In a large bowl, toss the mushroom mixture with the stale bread until well mixed, then transfer to the baking dish and spread into an even layer.
Whisk the eggs in the bowl until pale yellow, then whisk in the cream, milk, nutmeg, 1/2 teaspoon salt and 1/4 teaspoon pepper. Slowly pour over the bread mixture 1 cup at a time, giving it time to absorb between additions. Cover with aluminum foil and bake until it is puffed and set, about 45 minutes.
Crumble the fried onions and green bean chips together. Remove the foil from the pudding and spread the crumbs across the top. Bake until the onions are golden brown, about 5 minutes more.