Slice the tomatoes in half lengthwise and sit them in a roasting dish, cut side up (I usually leave them just attached to their 'pair' to help stay flat but not needed).
Sprinkle over the oregano, salt and pepper then drizzle over the olive oil.
Roast for approximately 1 ½ - 2 hours (depending on the size of the tomatoes) until they look a bit shriveled but not browning or too dry. If not using right away, they can be stored in the fridge, under olive oil if storing more than a day or two.
Video
Notes
Note - this recipe makes a relatively small quantity, enough for around 4 people to use on sandwiches etc or for 1-2 pasta dishes. Multiply up quantities as needed.