Combine lemon juice, coriander, pepper flakes, salt and ground pepper. Beat in oil. Store in refrigerator. Cook sweet potatoes in salted, boiling water just until tender, 20 to 30 minutes. Cool; peel and cut into 3/4-inch cubes. Combine potatoes, green pepper, onion, peanuts and cilantro. Gently toss with reserved dressing. Chill.