Place potato slices and water in a shallow microwave-safe casserole.
Cover with vented plastic wrap and microwave on high for 6 minutes.
Let stand for 3 minutes.
Sprinkle potatoes with tomatoes, scallions, green pepper, cumin, chili powder, oregano, and cheese.
Cover with vented plastic wrap and microwave on medium for 3 minutes.
Remove plastic wrap and run casserole under the preheated broiler for 2 minutes or until lightly browned.