Preheat oven to 350°. Spray a 13x9-inch baking dish with cooking spray.
In a medium skillet, melt ¼ cup butter over medium-high heat. Add yellow onion, celery, bell pepper, and green onion; cook until softened, 3 to 4 minutes. Add spinach, parsley, sage, thyme, and garlic; cook for 1 minute. Transfer to a large bowl, and add cornbread, bread crumbs, Creole seasoning, salt, and black pepper; stir until combined.
Coarsely chop any large oysters, and pat dry. Add oysters, 1 cup reserved oyster liquor, broth, eggs, and lemon juice to cornbread mixture; stir gently. Spoon into prepared pan. Drizzle with melted butter. Loosely cover with foil.
Bake for 15 minutes. Uncover and bake until bread is lightly browned and oysters are curled around edges, about 30 minutes more. Let stand for 10 minutes before serving.
Recipe by Louisiana Cookin' at https://louisianacookin.com/6-recipes-for-a-christmas-eve-feast/