Wash all jars, lids etc in the dishwasher.
Always wear gloves while preparing salsa!
Prepare tomatoes by soaking tomatoes in boiling water for 2-3 minutes to split and loosen skins. Peel and chop all tomatoes, drain excess juices off in a strainer or colander before adding to extra large bowl. (I half or quarter the tomatoes, then process briefly in a food processor before draining off juices, I like the tomatoes kind of chunky).
Dice or cube all onions and peppers into the same bowl. Add chopped cilantro. (I do all the onions, peppers and cilantro in a food processor - I keep them kind of chunky also).
Once all the vegies are in the bowl, stir in the lemon juice, garlic powder, salt and pepper.
Taste to see if it is as hot as you would like it - if not add 1-2 more hot peppers tasting after each addition. Keep in mind as it sits for a while it will get a little bit hotter.
Fill jars leaving about 3/4 inch at the top. Wipe off tops of the jars before putting lids on. Screw lids tight then turn back about 1/4 turn.
Process in steam canner (not pressure cooker / steamer) or boiling water bath for 15 minutes.
Before storing, test each jar to be sure it has sealed by pressing down on lid, it should not move.