Prepare the Chestnuts: Preheat the oven to 400°F. Cut a cross on the flat side of each chestnut with a sharp knife. Roast them in the oven for about 15-20 minutes. Peel and chop them into small pieces.
Sauté the Aromatics: In a skillet, heat the olive oil over medium heat. Add the chopped onion and minced garlic. Sauté until the onion is soft and translucent.
Combine Ingredients: Add the chopped chestnuts, dried oregano, vegetable broth, salt, and pepper to the skillet. Stir well to combine all the ingredients.
Bake the Casserole: Transfer the mixture to a baking dish and bake in the preheated oven at 350°F for about 25-30 minutes, or until the casserole is heated through and fragrant.
Serve: Remove the casserole from the oven and let it cool slightly before serving. Garnish with fresh oregano leaves, if desired. Enjoy your delicious Chestnut Casserole with Oregano!