Bring lentils, orange peel, white wine and water to boil over high heat. Lower heat to a simmer and cook for about 30 minutes or until lentils are just tender. When tender, drain off all liquid and discard orange peel.
While lentils are still warm, place in a bowl and stir in ¼ cup orange juice, vinegar, olive oil, roasted garlic, mustard, salt and pepper. Taste and adjust seasonings. Cover and set aside to marinate.
Place remaining orange juice, cognac, butter and grated orange rind in a heavy sauté pan over medium heat. Cook, stirring constantly, for about 5 minutes or until reduced by half. Add scallops and sauté for about 4 minutes, turning frequently, or until scallops are just warmed through. Remove from pan and keep warm.
Place a mound of lentils in the center of serving plates. Surround the lentils with watercress and lay four scallops on the greens at the "twelve", "three", "six" and "nine" o'clock positions. Drizzle any pan juices over scallops and sprinkle with toasted walnuts. Serve immediately.