Heat olive oil in a 5- or 6-quart enameled cast iron casserole or Dutch oven.
Add eggplant, zucchini, and onions and saute for 5 minutes until lightly golden.
Add the remaining ingredients to pot; stir gently but thoroughly and simmer, covered, for 30 minutes, stirring occasionally.
Remove lid and simmer for about 10 minutes more or until thick (this will depend on the juiciness of the tomatoes). If needed add paste to thicken.Spoon relish into hot sterlized jars leavin 1/2 inch headspace.
Remove air bubbles.Wipe rims and cap.
Place jars on rack completely covering the jars with 1-2 inches of water, heating the water to a rolling boiling (212 degrees f).Process in a boiling water bath for 15 minutes for half-pint (250 mL) jars and 20 minutes for pint (500 mL) jars. Adjust times for altitude.
Remove and leave in draft free place 24 hour.check for sealing and lable.If a jar is not sealed, refrigerate and reprocess within 24 hours or refrigerate and consume within three days.Store out of light in a cool dry place.
Serve at room temperature in a bowl surrounded by sliced French or Italian bread or cucumber rounds, or as a salad on romaine leaves.