Lightly oil NON STICK surface of skillet or flat griddle. Lay tomato slices in a single layer and allow to cook for about 7 min, or longer for more caramelization. Once they start looking tender I use a fork and slide it under the slice to flip.
Once I flip I remove from or turn off heat.
NOTE: The longer you leave them on the first side cooking, the more caramelized they will get, but the softer they get too, that's why you want somewhat thick slices, they will hold up better.