Combine the couscous, boiling stock or water, and salt in a large bowl; cover with a plate. Let sit 5 minutes, then fluff with a fork.
Preheat the oven to 375 degrees. Heat the olive oil in a large skillet over medium heat. Saute the garlic and onion 10 minutes, or until tender. Add the drained tomatoes and cook 10 minutes more, stirring frequently. Stir the tomato mixture into the couscous and mix in the reserved tomato juice, basil, pine nuts, raw spinach, and pepper.
Spread half the couscous mixture into a 12 by 7 by 2-inch baking dish or other shallow (2 1/2 quart) baking dish. Sprinkle on the cheese, then top with the remaining couscous. Cover the dish with foil and bake 25 minutes, or until hot and bubbly.