Cut the stem and tops off the tomatoes. Using a small spoon and, if necessary, a paring knife, scoop out the seeds and interior ribs of the tomatoes until you are left with only the outer wall. Salt the insides well and turn the tomatoes upside down on a rack. Let them drain for a good 30 minutes or more. NB: If the tomatoes don't stand up on their own, slice a very thin layer off their bottoms to form a flat surface.
While the tomatoes are draining, combine all the stuffing ingredients (along with the one or more of the optional ingredients if using) in a large bowl, mixing well. Keep the stuffing in the fridge until you're ready to use it.
When the tomatoes have had time to drain, wipe their insides gently with a paper towel. Spoon the stuffing inside each of the tomatoes. Don't be afraid to pile it on! If you like, you can add the tops back on as a kind of 'hat' for the stuffed tomatoes.
Serve at room temperature. If making ahead, keep them in the fridge, take them out a few minutes before serving.