Slice the tomatoes and hearts of palm into bite sized pieces, if the tomatoes are really gooey you may want to discard the seeds and some of the watery pulp. Dice the parsley and add it to the mix. Squeeze in the juice of the half a lemon, a dash of salt, and a drizzle of both the olive oil and balsamic to the bowl. Wait on adding the onions to the mix until they are room temperature. This will keep them from wilting the parsley and stop you from burning yourself when you slice them into bite size pieces.