Combine ingredients: Whisk lemon juice, harissa, and salt in a medium bowl; gradually whisk in oil. Add beans, carrots, dill, and parsley; toss to combine.
Refrigerate and serve: Transfer to an airtight container and refrigerate for at least 8 hours and up to 12 hours. Bring to room temperature for 15 minutes before serving. Taste and add more salt, if desired.
