For the dressing: Add the parsley, spinach, chives, tarragon, garlic, mayonnaise, canola oil, lime juice and vinegar to a blender. Blend until it resembles an emulsified dressing consistency. If it's too thick add a splash of water to loosen it up.
For the romaine hearts: Preheat a grill or grill pan to a medium heat. Whisk to combine the olive oil, lemon juice, salt and pepper in a small bowl; rub on the romaine leaves using your hands. Grill the romaine until nice and charred, 1 to 2 minutes per side.
For the shrimp: Pat the shrimp dry and toss with some canola oil in a bowl. Grill for 2 minutes on each side.
For the salad: Place the romaine halves on each plate, divide the shrimp on top, sprinkle with the croutons and drizzle with the dressing. Top with Parmesan.
Rubbing the lemon oil all over gives this lettuce a nice bright flavor to it.