Bake at 375 for 45 minutes.
Heat 1 tablespoon of the olive oil in a large skillet over medium-high heat. Stir in the onion, zucchini, half the garlic and 1/2 teaspoon salt and cook, stirring frequently, until the vegetables are softened and just beginning to brown, about 3 minutes. Increase the heat to high, stir in the couscous mixture and simmer rapidly, stirring frequently, until the couscous is just al dente and the liquid is beginning to thicken, about 5 minutes. Stir in the spinach and cook, adjusting the heat if necessary, until the leaves are bright green and just beginning to wilt, about 30 seconds. Set the filling aside to cool slightly.
To make the sauce, combine the remaining garlic and olive oil in a Dutch oven, add the chile flakes if using and stir to combine. Place the pot over medium-high heat and cook, stirring occasionally at first then more frequently as the oil starts to sizzle to prevent the garlic from burning, until the garlic starts to stick to the edge of the spoon and is just beginning to turn a very pale straw color, 2 to 3 minutes. Stir in the reserved drained tomatoes plus any accumulated juices, 1 cup water, 1/2 teaspoon salt and 1/2 teaspoon black pepper and cook, stirring frequently, until the mixture just begins to come together and thicken, about 3 minutes. Remove from the heat.
