For the chicken: In a small bowl, mash the rosemary, thyme, sumac and lemon zest with enough olive oil to get a smooth paste. Rub this paste all over the chicken. Season the chicken from high above (to ensure even distribution) with salt and pepper. Refrigerate 8 hours or overnight.
Place the chicken on a baking sheet (or large pan) with a rack. Allow the chicken to sit at room temperature for 1 hour (this will allow it to cook more evenly).
Preheat the oven to 375 degrees F.
Pour 1 cup of water in the bottom of the baking sheet and roast the chicken until it is deep golden brown and caramelized, and the thickest part of the leg registers 160 degrees F on a thermometer, 1 to 1 1/2 hours. Allow the bird to rest for 20 minutes (the temperature will continue to rise to 165 degrees F out of the oven).
For the vinaigrette: While the bird is resting, pour 4 tablespoons of the juices (depending on how rich you want the vinaigrette, you can reduce the juices first before measuring) into a large bowl along with the vinegar, shallots, mustard and tarragon. Drizzle in the olive oil. Toss in the lettuce and season with salt and pepper. Divide among 4 plates.
Carve the bird by removing the breast and legs from the carcass. Cut the 2 breasts into 4 pieces and separate the thighs from the drums on the legs, leaving you also with 4 pieces. Divide the chicken among the plates with the lettuce and serve.