Whisk together the oil, cranberry juice, mustard, agave nectar, vinegar, salt, and pepper in a medium bowl. Stir in the tarragon, if using. Place the beans in the bowl with the dressing, stir to coat, and set aside.
Place 1/8 cup of the bean mixture in the bottom of a short mason jar. Follow with 1 tablespoon feta, 1/2 tablespoon cranberries, 1/8 of the radicchio, and 1/8 of the red lead lettuce. Repeat with the remaining jars.