Prepare the rice: Cook the rice according to the package directions if it is not already prepared. Fluff with a fork and allow excess steam to escape.
Trim the broccoli: Wash the broccoli and cut it into long spears with sturdy stems. Trim away any tough ends so the pieces can stand upright.
Steam the broccoli: Steam the spears until bright green and just tender but still firm. Cool briefly and drain thoroughly to remove excess moisture.
Cook the aromatics: Heat olive oil or butter in a skillet over medium heat. Add the chopped onion and cook for 5–7 minutes until softened. Stir in the garlic and cook for another 30–60 seconds.
Season the rice: Add the cooked rice, lemon juice, dill, mint, parsley, sunflower seeds, and shredded cheddar. Season with salt, black pepper, and optional cayenne. Fold gently to combine.
Prepare the baking dish: Preheat the oven to 350°F (175°C). Lightly grease a 9-by-13-inch baking dish and spread the rice mixture evenly inside.
Arrange the broccoli forest: Insert the broccoli spears stem-first into the rice, spacing them evenly so they resemble little trees. Gently press the stems into the rice to help them stand.
Add the finishing touch: Drizzle the broccoli with melted butter or olive oil, if desired. Cover loosely with foil.
Bake the casserole: Bake for 15–20 minutes, or until the rice is heated throughout and the cheese has softened. Avoid overbaking to preserve the broccoli's color and texture.
Serve warm: Let the casserole rest for a few minutes. Serve portions of seasoned rice with several broccoli spears.