Preheat a grill to medium-high. Arrange pickles and red onion on the grate, cut-sides-down, and grill until lightly charred and blackened in spots. Grill the bell pepper, turning occasionally, until lightly charred all over.
Meanwhile, combine equal parts sugar and vinegar and season with a shake of red pepper flakes to taste.
Once the pickles and vegetables are ready, remove from the grill to cool slightly. Finely chop, then stir into the vinegar mixture.