Combine the quinoa, broth, and seasoning in a saucepan. Bring to a slow boil, then lower the heat, cover, and simmer gently until the water is absorbed, about 15 minutes.
Meanwhile, heat the oil in a large skillet. Add the onion and sauté until golden. Add the broccoli and enough water to keep the skillet moist. Cover and steam until the broccoli is tender-crisp, about 5 to 7 minutes.
In a mixing bowl, combine the cooked quinoa with the broccoli mixture, dried tomatoes or olives, and half of the cheese. Season with salt and pepper and stir well.
Transfer the mixture to a lightly oiled, shallow two-quart casserole. Arrange the tomato slices over the top. Sprinkle evenly with the remaining cheese.
Bake until the top is golden and crisp, about 20 to 25 minutes. Let the casserole stand for 5 minutes, and serve.