Heat oven to 450 degrees. In a 9-inch baking dish, cake pan or gratin dish, toss together tomatoes, scallions, 2 tablespoons oil, 1 tablespoon vinegar, garlic, 1/2 teaspoon salt, pepper and oregano sprigs. Roast until tomatoes are tender, about 15 minutes.
While tomatoes roast, heat the stock until it boils, then stir in remaining 1 teaspoon salt, adding more to taste. (You want a well-seasoned broth here to flavor the couscous.) Stir in cilantro, lemon zest and cumin.
Remove tomatoes from oven and fold in couscous, chickpeas and hot stock mixture. Cover pan tightly with foil, and return to oven for 20 minutes.
Remove foil and fold in about 3/4ths of the feta (save the rest for garnish) and Parmesan. Bake uncovered until feta starts to melt, another 5 minutes.
To serve, pull out and discard herb sprigs if you like, and spoon couscous into bowls. Top with remaining feta, lots more herbs, pepper and a drizzle of olive oil and balsamic vinegar.