Sprinkle the zucchini slices all over with 1/2 teaspoon salt. Set aside. Stir together the beans, pico de gallo and oregano in a medium bowl.
Arrange the following in layers in a 9-inch deep-dish pie pan or 10-inch round microwave-safe dish: 4 of the tortilla halves, one-third of the bean mixture, one-third of the zucchini and 1/4 cup of the cheese. Repeat twice, while packing down the layers. Sprinkle with additional salt and the remaining 1/4 cup cheese.
Microwave on high until the zucchini is fully cooked, about 10 minutes. Remove from the microwave and loosely cover with foil to finish the cooking process, about 5 minutes. (Alternatively, preheat the oven to 375 degrees F, cover the baking dish with aluminum foil and cook until heated through and the cheese is melted, 15 to 20 minutes.)
Sprinkle with the cilantro, slice into 4 wedges and serve.