To prepare a sweet green tomato relish, pulse 8 to 10 quartered green tomatoes and 2 to 4 quartered white onions in a food processor until they are finely chopped. Place the vegetables in a large saucepan.
Stir in 12 ounces of orange marmalade, 1 cup of cider vinegar, 4 cups of brown sugar and 1/4 teaspoon of crushed red pepper. Bring the relish to a boil. Reduce the heat and simmer the mixture, uncovered, for 1 to 2 hours until the relish turns golden brown.
Pour the relish into clean, sterilized canning jars. Completely fill the jars, checking for air pockets. Place the jars in a large stockpot filled halfway with boiling water and cook them for 10 minutes.
Remove the jars from the pot. Store the relish for up to 1 year.
To make a sugar-free version, combine 2 pounds of chopped green tomatoes and 1 pound of chopped white or yellow onions in a large non-aluminum stockpot. Add 1/4 pound of chopped red peppers, 1/2 pound of chopped tart cooking apples and 6 finely-chopped garlic cloves. Stir in 1/2 to 1 cup of apple cider vinegar and 1 tablespoon of kosher salt.
Bring the mixture to a boil. Reduce the heat and simmer the relish for 1 hour until the mixture has thickened. Add 4 finely-chopped Jalapeño peppers, 2 tablespoons of chopped cilantro and 1 teaspoon of ground cumin. Simmer the mixture for 5 minutes. Store the relish in the refrigerator for up to 2 months.