Spray a 9x13" pan with nonstick cooking spray, set aside.
In a large nonstick pan, heat the oil, add the beef, bell peppers and scallions. Cook, stirring as needed, until the beef is browned and the vegetables are softened, 6-8 minutes.
Add tomatoes, spices and salt, cook, stirring as needed until the flavors are blended, about five minutes.
Arrange alternate layers of the potatoes and beef mixture in the baking dish. Cover with foil and bake 40 minutes, uncover and sprinkle evenly with the cheese. Bake until the potatoes are cooked through and the cheese is melted, about 10 minutes longer.