For the tomato relish, rinse the tomatoes, quarter them and remove the stalks. Peel and dice the onions and garlic. Heat oil and sauté onions and garlic until translucent.
Rinse chili peppers, slice lengthwise and remove seeds. Cut the peppers into rings. Add to the saucepan with the tomatoes and sauté, stirring, until soft, about 15 minutes.
Rinse celery leaves and cut into thin strips. Rinse thyme and strip leaves from stems.
Add both to the tomatoes with bay leaves, mustard and sugar, vinegar, coriander seeds and salt and steam for another 20 minutes, stirring occasionally.
Pour the tomato relish into prepared jars and close tightly.