- Build charcoal fire for direct grilling and preheat to 500 degrees.
- In medium saucepan, combine 1¼ cups water, vinegar, sugar, and salt. Cook over medium-high heat until sugar dissolves, about 4 minutes. Remove pan from heat, cover, and set aside.
- Grill cucumbers over hot coals until they char and slightly soften, about 2 minutes on each side. Divide cucumbers and onions among 3 hot sterilized pint jars. Add 2 sprigs dill, garlic, and 1¼ teaspoons red pepper flakes to each jar. Pour pickling liquid evenly into each jar and tighten the sterilized lid. Let cool to room temperature before refrigerating. Serve chilled.
- Pickles will keep refrigerated for 4 weeks.