Preheat the oven: Set to 375°F (190°C).
Lightly oil a 9x13-inch baking dish.
Rinse the rice: Rinse under cold water until it runs mostly clear. This helps prevent mushy rice.
Prep the veggies: Dice the onion and bell pepper. Mince the garlic.
Chop broccoli into small, bite-size florets.
Make the sauce: In a large bowl, whisk plant milk, vegetable broth, coconut milk or cashew cream, tomato paste, nutritional yeast, soy sauce, lemon juice, smoked paprika, thyme, turmeric, cumin, red pepper flakes, 1 teaspoon salt, and a few grinds of black pepper.
Assemble in the dish: Add rinsed rice, onion, bell pepper, garlic, broccoli, peas and carrots, corn, and beans to the baking dish. Drizzle with 2 tablespoons olive oil. Pour the sauce over everything and stir well to distribute.
Cover and bake: Tightly cover the dish with foil.
Bake for 35 minutes.
Make the topping: In a small bowl, mix panko (and nuts if using) with 2 tablespoons olive oil and a pinch of salt until evenly moistened.
Uncover and finish: Remove foil, gently stir the casserole to loosen the rice. Sprinkle the topping evenly. Bake uncovered for 10–15 more minutes, until the rice is tender and the top is golden.
Rest and garnish: Let it sit 8–10 minutes.
Taste and adjust salt, then finish with chopped parsley or chives and a squeeze of lemon if you like.