Prep all ingredients per the instructions above.
Preheat the oven to 350℉ (176℃). Cook the tilapia on a baking sheet to an internal temperature of 145℉ (63℃). Set aside to cool completely.
Slice the rolls lengthwise and lightly toast until just warm and slightly crisp.
In a small bowl, mix the mayonnaise and Dijon mustard. Season with black pepper to taste.
Spread the mayonnaise–mustard mixture evenly inside the rolls.
Layer with onion, sliced pickles, parsley, chives, and tilapia into the rolls.
Add the lemon slices to the sparkling water and gently stir. Add ice cubes as desired.
Serve the broodje haring with potato chips, pickle spears, cherries, and lemon sparkling water.