Cut the tomato in half, this can be straight through the stem area or at 90 degrees through the equator for want of a better describing word. Either way make sure any hard bits related to the stem are removed so those eating it don't need to spit it out.
Heat a frying pan to a medium temperature, tomatoes have a lot of sugar so if it is too hot it will just burn the outside and still be firm in the middle.
Season the cut side of the tomato with salt and pepper. Add the oil to the frypan, then immediately add the tomato cut side down. This helps hold the tomato together after turning it, essentially all the tomato juices run into and stay in the skin.
When the cut edge of the tomato is softened and nicely browned; about 15 minutes, turn. Yes, this takes a while so don't be tempted to add quick cooking items you plan to serve with them otherwise they won't have time to cook.
Cooking the skin side takes longer, about 20 minutes, thus ensuring it is cooked all the way through; meaning soft and sweet. Serve while still hot.