Position one rack on the lowest shelf in the oven and preheat to 425°F. Combine the eggplant and peppers in a large bowl. Add 3 tablespoons of the oil and toss to coat. Sprinkle with salt and pepper. Arrange the vegetables in a single layer on a large rimmed baking sheet. Roast on the lower oven rack until tender and starting to brown on the bottom, stirring after 12 minutes, about 25 minutes total. Remove from the oven.
Meanwhile, heat the remaining 2 tablespoons oil in a 12-inch skillet over medium heat. Add the onion and dried crushed pepper and sauté until the onion begins to brown, stirring occasionally, about 6 minutes. Add the tomatoes with their juices and 1½ tablespoons of the marjoram. Break up the tomatoes with a spoon. Simmer the sauce until it is thick and the flavors blend, stirring occasionally, about 25 minutes.
Add the eggplant, peppers, olives and capers to the sauce. Mix in the wine and bring to a simmer. Season the sauce to taste with salt and pepper. Sprinkle the tuna with salt and pepper. Add to the sauce and simmer until just cooked through, about 5 minutes.
Spoon quinoa onto 2 plates. Spoon all the fish, and generous servings of the sauce and vegetables atop the quinoa. Sprinkle with additional marjoram and serve right away.