Prepare the steamer by filling the base with water according to manufacturer's directions.
Combine the couscous, 11/2 cups water, 2 tablespoons of the olive oil, 1/2 teaspoon of the salt, and 1/4 teaspoon of the pepper to taste in the plastic cooking insert and place in one of the steamer baskets. Combine the Brussels sprouts, cauliflower and carrots into the other basket. Set the cooking plate on top of the baskets. Season the salmon with 1/2 teaspoon of the salt, 1/4 teaspoon pepper, and the Essence. Place the salmon on the cooking plate and place the steamer top on. Set the timer for 12 minutes. Cook the salmon and couscous, undisturbed, until the timer goes off.
While the salmon and couscous are cooking, make the tomato sauce. In an oven-proof, baking dish, place the tomatoes, garlic cloves, lemon juice, lemon zest, marjoram, 1/2 teaspoon salt and 1/4 teaspoon ground black pepper and toss well to blend. Place the pan under the broiler and cook until wilted and the tomatoes are caramelized, about 10 to 12 minutes. Remove from the oven and serve while hot.
When the timer goes off, the salmon should be just cooked through, moist and tender. Remove the salmon from the steamer. Remove the vegetables from the steamer and season lightly with salt and pepper. Allow the couscous to remain in the steamer until the steamer goes off, about 4 minutes longer. Remove the couscous and fluff with a fork. Serve the salmon fillets over the warm couscous, with the tomato sauce spooned over the top of the salmon and the vegetables on the side.