This is a recipe my sister used, but I have never made it.
Green Tomato Relish
12 green tomatoes
6 TBSP salt
24 green peppers
6 red peppers
12 large onions
4 quarts boiling water
1 quart vinegar
3 cups sugar
1 tsp celery seed
1 tsp. mustard seed
Cut tomatoes up fine; add salt and let stand for 1 hour; drain. Put peppers and onions through coarse food chopper, pour 2 quarts boiling water over peppers and onions; then drain at once. Pour over 2 remaining quarts of water; let stand 10 minutes; then drain. Add tomatoes, vinegar, sugar and spices. Let come to a boil and cook 30 minutes. Use stainless or enameled pot. Put into sterilized jars while hot and seal.