Chop all your ingredients as fine as you want them. Remove seeds if you prefer.
Add salt and cumin and stir everything together. If you like, add the juice of 1/2 of a lemon or a lime. Lime is better, but lemon is fine. Keep in mind that the salsa will be a little more sour after it ferments, so taste after adding a little juice to make sure it isn't too sour.
Scoop the salsa into a clean glass jar. Make sure there is enough liquid to cover everything. If there isn't, add a bit more. You can use a fermenting weight to keep everything submerged if you have one. If not, just make sure there is plenty of liquid.
Keep at room temperature for a few days. I usually do 2-3 days, but you can do just one or let it go a bit longer if you like. Open the jar each day and check that the salsa is submerged. You will see some bubbles as it ferments, and you may see a white film over the top. This is harmless and you can skim it off. If you get pink, black, or green things, or fuzzy things, growing, it spoiled somehow. Probably there either was too little salt or the salsa wasn't under the brine at the top.
Once you are happy with the salsa's level of fermentation, go ahead and serve it or put it in the refrigerator to mostly stop the fermenting process. There will be a lot of liquid since you used brine. I don't drain it, but leave it in the jar and scoop out the salsa itself.