Spray a 9x13 baking dish with nonstick spray, and spread about a third of the tomato sauce over the bottom. Lay half the ravioli in a single layer over top. Sprinkle with the spinach and half the cheese, another third of the sauce and then the remaining ravioli, sauce and cheese. Cover with foil and bake for 20 minutes, then uncover and bake another 10 minutes, until golden and bubbly.
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