Tatemado is a little more than roasted or grilled. Maybe "chargrilled" or "blackened" is better? Basically you want it cooked, but slightly burned. You can do this on a comal (griddle), over a flame, or directly on some hot coals. You want to cook the chiles and blacken the skin, but not burn it through to the flesh. Some recipes will tell you then to remove all or some the blackened skin, some will tell you to leave it. The charring deepens the flavor profile and imparts a slight smokiness.