Slice heirloom tomatoes, and half the cherry tomatoes. Dice the shallot and cut basil into fine pieces.
Assemble the tomatoes and shallots in a bowl or large plate. Drizzle olive oil and balsamic vinegar (if using), and sprinkle basil, salt, pepper, parsley, and crushed red pepper over the top (evenly coating as much as you can).
Give the salad a quick toss and serve. This will last up to an hour before the heirloom tomatoes will start to soften. Enjoy!
I use an aged balsamic here. It has a much sweeter flavor and is more syrupy than everyday balsamic vinegar. If using balsamic vinegar, use aged or use a glaze, otherwise this salad will likely be too acidic.