Sprinkle the courgette slices all over with 1/2 teaspoon salt. Set aside. Stir together the beans, salsa 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 courgette 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 190°C, cover the baking dish with aluminum foil and cook until heated through and the cheese is melted, 15 to 20 minutes.)
Sprinkle with the coriander, slice into 4 wedges and serve.