To make the salsa, remove stalks from the tomatoes, then cut them into quarters if they are small and eighths if they are larger. Place with all the other salsa ingredients in a bowl and mix. You can use this right away or set aside for several hours in the refrigerator
Place the ancho chilies in a medium pot, cover with water and bring to the boil. Remove from the heat, push the chilies into the water so that they are all submerged and set aside to soften for 15 minutes.
Lift the chilies out of the pot and reserve the liquid. When the chilies are cool enough to handle, pull off the stalks and scoop out the seeds, keeping the chilies whole.
Put the cheese, chives and oregano in a bowl and mash with a fork to mix. Stuff the chilies with the cheese mixture and pinch closed. Arrange the stuffed chilies in a single layer in a steamer basket. Pour enough of the reserved liquid into the steamer to make a 3/4-inch layer (make up with water if necessary). Steam for 15 minutes or until the chilies puff out and are tender. Transfer to a platter and surround with the salsa.