1. Combine coriander and fennel seeds in small, dry skillet and toast over medium-high heat until seeds are golden and fragrant, 3 to 4 minutes, shaking and moving pan in circular motion occasionally at first, then constantly. Transfer seeds to plate to cool.
2. Make seasoning mixture in food processor by pulsing toasted coriander and fennel seeds with herbs and garlic until finely chopped. Add salt and pepper and whirl until all ingredients are very finely chopped, 30 seconds. With motor running, drizzle in oil. Set seasoning mixture aside for 15 minutes.
3. While seasoning sits, use your fingers to gently separate skin from turkey breast meat, taking care not to tear skin. Using your hand, rub one third of seasoning mixture under skin on each side of breast and coat inside of breast with remaining mixture. Rub your oily hands over skin, coating it lightly. Seal breast in plastic wrap and set on a plate. Marinate breast in refrigerator for 4 hours.
4. Preheat oven to 350 degrees F. Place rack in large roasting pan. While oven heats, unwrap turkey and let sit on counter.
5. Pour chicken broth into roasting pan. Set turkey breast on rack. Roast turkey, turning pan in oven every 20 minutes to help it brown evenly. Breast is done when instant read thermometer inserted into thickest point reads 165 degrees F., about 2 hours for a 6 pound breast (allowing 20 minutes per pound). Skin can be dark without meat being dry, but tent foil over breast if skin is getting too dark. Because of brining effect of seasoning paste, skin near bone may look pale pink.
6. Let breast rest for 20 minutes before carving. Strain juices to serve on the side.

* May use 4 cup combination of low-sodium chicken broth and water.