Step 1: Prepare the Stuffing
1. Sauté Vegetables: In a skillet, heat a tablespoon of olive oil over medium heat. Add the chopped onion, celery, and mushrooms (if using). Sauté until softened, about 5–7 minutes.
2. Combine Ingredients: In a large bowl, combine the sautéed vegetables with the bread cubes, dried cranberries or raisins, slivered almonds or walnuts, dried thyme, dried sage, and chicken broth. Mix until the bread is evenly moistened. Season with salt and pepper to taste.

Step 2: Prepare the Hens
1. Preheat Oven: Preheat your oven to 375°F (190°C).
2. Season Hens: Pat the Cornish game hens dry with paper towels. Rub the outside of each hen with olive oil and season generously with salt, pepper, garlic powder, onion powder, dried thyme, and dried rosemary.

Step 3: Stuff the Hens
1. Fill Hens: Carefully stuff each Cornish game hen with the prepared stuffing, packing it lightly. Tie the legs together with kitchen twine and tuck the wings under the body to ensure even cooking.

Step 4: Roast the Hens
1. Place in Baking Dish: Arrange the stuffed hens in a roasting pan or baking dish. You can add some broth or water to the bottom of the pan if you want them extra moist.
2. Roast: Roast in the preheated oven for about 50–60 minutes, or until the internal temperature reaches 165°F (74°C) and the juices run clear. Baste the hens with the pan juices halfway through cooking.

Step 5: Serve
1. Rest: Remove the hens from the oven and let them rest for about 10 minutes.
2. Garnish: Garnish with fresh parsley and serve.