Follow these simple steps to assemble and bake your delicious Veggie Rice Casserole:

1. Preheat Oven & Prepare Dish: Preheat your oven to 375°F (190°C). Lightly grease a 9×13 inch (or similar capacity) baking dish with butter or cooking spray.
2. Sauté Aromatics: Heat the olive oil in a large skillet or Dutch oven over medium heat. Add the chopped onion and sauté for 3-4 minutes until softened. Add the minced garlic and cook for another minute until fragrant, being careful not to burn it.
3. Cook Harder Vegetables: Add the diced carrots and chopped bell peppers to the skillet. Cook for 5-7 minutes, stirring occasionally, until they begin to soften.
4. Add Softer Vegetables: Stir in the broccoli florets, diced zucchini, and sliced mushrooms. Cook for another 5-7 minutes, until the mushrooms release their liquid and the vegetables are tender-crisp. You don’t want them to be mushy, as they will cook further in the oven.
5. Combine Wet Ingredients & Seasonings: In a small bowl, whisk together the vegetable broth, heavy cream (or milk), soy sauce (or tamari), dried Italian herbs, salt, and black pepper.
6. Combine Rice and Vegetables: Remove the skillet from the heat. Add the 4 cups of cooked rice to the skillet with the sautéed vegetables. Pour the broth mixture over the rice and vegetables. Gently stir everything together until well combined.
7. Add Cheese (Part 1): Stir in 1 cup of the shredded Cheddar cheese into the rice and vegetable mixture. Mix until it’s evenly distributed.
8. Transfer to Baking Dish: Carefully transfer the entire mixture into the prepared baking dish, spreading it out evenly.
9. Top and Bake: Sprinkle the remaining 1/2 cup of shredded Cheddar cheese and the 1/2 cup of Parmesan cheese evenly over the top of the casserole. If using, sprinkle the Panko breadcrumbs over the cheese for added crunch.
10. Bake: Place the baking dish in the preheated oven. Bake for 20-25 minutes, or until the casserole is heated through, the cheese is melted and bubbly, and the top is golden brown. If the top starts to brown too quickly, you can loosely tent it with aluminum foil.
11. Rest and Serve: Remove the casserole from the oven and let it rest for 5-10 minutes before serving. This allows the casserole to set slightly, making it easier to serve and preventing burns from super hot cheese. Garnish with fresh parsley or chives if desired.