How to Make It
Light a grill or preheat a grill pan. Finely chop the cabbage in a food processor and transfer to a large, heavy pot. Put the tomatoes, bell pepper and onion in the processor and finely chop; add to the cabbage. Add the vinegar, sugar, celery seeds, turmeric, cayenne and 1 1/2 teaspoons of kosher salt to the pot and bring to a boil over high heat. Cook the chowchow over moderate heat, stirring occasionally, until it's cooked down to about 2 cups, about 10 minutes.
Meanwhile, form the ground beef into 4 patties and season with salt and pepper. Grill the burgers until nicely charred outside and medium-rare within, about 3 minutes per side. Grill the buns, cut side down, until toasted, about 20 seconds.
Set the grilled hamburgers on the bottom halves of the buns. Spoon a thick layer of chowchow on the burgers, top with the toasted buns and serve.