Roma: Cut off the stem end, slice the tomatoes in half. Cut each half into thin slices from stem to end. Then, cut those pieces across into small, diced pieces. I also cut off any of the edible tomato flesh from around the stem piece you cut off earlier. I think this is easier than 'coring' the tomato. Add the pieces to the mixing bowl.
Onion: Cut the onion in half and slice off the root end. Then, remove the skin. Slice the onions in thin strips from tip to root. Cut the thin slices across to make small, diced pieces. Add them to the mixing bowl.
Jalapeño pepper: Cut the stem off. Slice the pepper lengthwise. Carefully remove the white ribs and seeds - do not touch your eyes after handling these peppers. Cut the pepper half into strips, then cut those pieces across into petite diced pieces. Add the peppers to the mixing bowl. Please remember to wash your hands!
Lime: Cut each lime in half across the middle (not end to end). Using a juicer or a fork (twist the fork inside the pulp), squeeze juice. I like to squeeze the juice into a measuring cup or small bowl, then into the measuring spoon. Add the juice to the mixing bowl.
To the mix, add salt and stir until well combined. Serve with corn chips, use to top burritos or tacos, or chill until ready to serve.