With the back of a spoon, mash together some whole-grain mustard, diced fresh ginger, and diced jalapeno. Incorporate date sugar, lemon juice, and champagne vinegar to form a loose paste. Whisking constantly (or using a food processor), pour extra-virgin olive oil in a steady stream to emulsify.
Slice tomatoes in thick slabs. Add to vinaigrette, spooning up juice until coated completely, and allow enough time for the tomatoes to absorb the flavor of the vinaigrette. Plate on a bed of fresh arugula and sprinkle with fresh parsley. Serve at room temperature with juice from marinade on the side.