- Cut each of the fish fillet into 2 pieces. Season with salt and pepper.
- Mix together the dry ingredients for the batter and set aside.
- For the Chutney: Combine onion, vinegar and sugar in sauce pot and cook on medium heat until reduced by ¾. Add the watermelon and Fresno chiles, and continue to cook for 5 more minutes until thickened. Cool and add the herbs, strain any excess liquid as needed.
- For the Tartar Sauce: Squeeze any excess water from the watermelon rind. Combine all ingredients and mix well. Keep cold.
- Mix dry ingredients from earlier, with the sparkling water and lemon juice until just combined. Do not overmix.
- Dry the fish well, coat with flour, and dip into the batter.
- Fill a pot with the oil so that it reaches ½ way up the sides and heat to 350°F.
- Place fish into the heated oil and fry until golden brown, about 3-4 minutes. Season with salt while warm.
- Serve fish with the tartar sauce and the chutney. Garnish the plate with a slice of watermelon.