Wear gloves to handle the chilies and combine the chopped tomatoes, chilies, oregano, cumin, garlic and onions together.
Place the tomato mixture little by little in your fermentation jar, pounding it vigorously and sprinkling some of the sea salt as you go.
Make sure the mixture fills the jar up to no more than 1 inch below the top (because of the expansion), adding more if needed, and that the extracted water covers the vegetables entirely.
Press the mixture and keep it under the brine by placing a plate or a lid on top weighted down by a rock or a jug of water. Cover with a clean towel if needed to keep out fruit flies.
Place the fermentation jar in a warm spot in your kitchen and allow the salsa to ferment for 3 to 5 days.
Check on it from time to time to be sure that the brine covers the mixture and to remove any mold that may form on the surface.
A good way to know when it’s ready is to taste it during the fermentation process and move it to the refrigerator when you’re satisfied with the taste.