1 tbsp. ground cumin 1 lb. cherry tomatoes 1/2 tsp. grated fresh ginger Zest and juice of 1/2 lemon 1/2 cup brown sugar 1/2 cup water 1/2 medium onion, sliced 1/2 tbsp. vegetable oil
Make the tomato jam: In a medium heavy pot, combine all the ingredients over high heat. Let the mixture to come to a boil, stirring occasionally, then reduce the heat to low. Simmer until the jam thickens, about 1 hour. Let cool completely, then transfer to the refrigerator for at least 3 hours, or overnight.
Make the grilled cheese: Heat and add the oil. Add the onion slices and cook over moderate heat, stirring occasionally, until soft and golden, about 10 minutes. Transfer to a bowl. Wipe off the pan with a paper towel.
Butter one side of each slice of bread. Flip the slices so they are all butter-side down on the work surface. Smear a generous layer of tomato jam on half of the bread slices, and top with 1 to 2 tablespoons of caramelized onions. On the other bread slices, place 2 to 3 slices of cheese.
Set the pan over moderate heat. Working in batches, take the bread slices with the cheese and place butter-side down in the pan and toast for about 3 minutes, until the cheese is melted and the bread is browned. Set the toasts cheese-side down on the caramelized onion slices. Transfer the whole sandwich back to the pan, un-toasted side down, and cook until for 2 to 3 minutes, until brown. Give the sandwich a firm pat with the spatula, to make sure the cheese is sticking to the onions, and remove from heat. Repeat with remaining sandwiches.