If the tomato skins are thick you can peel them by dipping the tomatoes into boiling water for 30 seconds then plunging them into cold water. The skins will slip off.
Chop tomatoes and combine with chopped onion, celery, jalapeño chili peppers, vinegar, mustard seed, coriander seed, salt and pepper.
Cover and refrigerate several hours or overnight, stirring occasionally.
Note: This recipe is kid-friendly and super mild. If you want to add a little more "heat", just add a few more jalapeño chili peppers. :)
Recipe by LemonPeony at https://lemonpeony.com/easy-pico-de-gallo-recipe-without-cilantro/