Prepare the Wild Rice: Cook the wild rice blend according to the package instructions. Set aside.
Cook the Chicken: Season chicken pieces with salt, pepper, and paprika. Heat 1 tablespoon olive oil and 1 tablespoon butter in a large skillet over medium-high heat. Add the chicken and cook until lightly browned and cooked through, about 5-7 minutes. Remove and set aside.
Sauté the Vegetables: In the same skillet, heat remaining olive oil and butter. Add onions, celery, carrots, and mushrooms. Sauté until softened, about 5-7 minutes. Stir in garlic and cook for another minute. Remove from heat.
Make the Cream Sauce: In a large saucepan, heat butter and olive oil over medium heat. Whisk in the flour and cook for 1-2 minutes until lightly golden. Gradually add chicken broth, whisking constantly to avoid lumps. Stir in milk, chicken bouillon, Dijon mustard, Worcestershire sauce, and seasonings (parsley, basil, thyme, salt, and pepper). Simmer until thickened. Stir in 1 ½ cups cheddar cheese and Parmesan cheese until melted and smooth.
Combine and Assemble: In a large mixing bowl, combine cooked wild rice, chicken, sautéed vegetables, and the cream sauce. Mix until everything is evenly coated. Transfer the mixture to a greased 9x13-inch baking dish.
Add the Topping: Sprinkle the remaining ½ cup cheddar cheese over the casserole. If using the panko topping, mix breadcrumbs with melted butter and olive oil, then sprinkle over the cheese.
Bake: Preheat oven to 350°F (175°C). Bake the casserole for 25-30 minutes, or until golden and bubbly.
Serve and Enjoy: Let the casserole rest for 5 minutes before serving. Pair with a side salad or roasted vegetables for a complete meal.