Heat the oil in a large saucepan. Sauté the onion until translucent. Add the green pepper and continue to sauté until it has softened and the onions are golden.
Stir in the crushed tomatoes and seasonings, black beans, and zucchini. Bring to a simmer, then simmer gently for 5 minutes.
Layer as follows in a lightly oiled 9 x 13 inch or 2-quart round casserole dish: half of the tortillas, half of the tomato-black bean mixture, and half of the cheese. Repeat.
Bake for 15 to 20 minutes, or until the cheese is bubbly. Let stand for 5 to 10 minutes, then cut into squares or wedges to serve.