This is good with charcoaled steak.

2 large purple onions, cut into 1/4-inch slices
6 large, firm tomatoes, peeled and quartered
1 bell pepper, seeded and cut into strips
3/4 cup cider vinegar
1/4 cup water
1 1/2 teaspoons celery seeds
1 1/2 tablespoons mustard seed
1/2 teaspoon salt
2 tablespoons granulated sugar
1/2 teaspoon cracked black pepper

Place onions, tomatoes and bell pepper in a bowl. In a saucepan, bring all other ingredients to a boil. Boil for 1 minute only. Pour over vegetables and chill.