Combine first 3 ingredients in a small bowl; set aside. Sprinkle fillets with sesame seeds, salt, and pepper, pressing mixture gently into fillets. Heat a large nonstick skillet coated with cooking spray over medium-high heat. Add fillets; sauté 4 minutes on each side or until fish flakes easily when tested with a fork.
Spread hoisin mixture evenly on top half of each roll. Arrange 1/2 cup watercress and 2 tomato slices over bottom halves of rolls; top each with a fillet and 1/4 cup sprouts. Cover with tops of rolls.