Thelma's Sandwich Spread

Now I don't remember ever having this, but mom says it was really good.

12 green peppers
12 red peppers
12 green tomatoes
2 large onions

Grind all together, add scant pint of water, 2 cups sugar, 1 heaping Tbsp. flour, 1 heaping Tbsp. celery seed, 4 heaping Tbsp. prepared mustard. Boil for 15 minutes, add quart of mayonnaise and seal in jars.