Rinse chile peppers. On a comal or in a dry skillet toast chile peppers over medium-high heat about 2 minutes or until fragrant, turning once. Remove stems, seeds, and membranes from chile peppers. Place chile peppers in a medium bowl and add enough boiling water to cover. Let stand for 10 minutes.
On the comal or in the dry skillet toast peppercorns, cloves, and cumin seeds over medium-high heat for 1 to 2 minutes or until fragrant; remove from heat. Transfer spices to a spice grinder; grind until finely ground.
Place the tomatillos, green tomato, onion, and garlic on the comal or in the dry skillet. Roast over medium-high heat about 7 minutes or until skins are blackened, turning occasionally. Remove from heat. Let stand until cool enough to handle; peel vegetables.
For yellow mole, in a blender or food processor combine drained chile peppers and peeled vegetables. Cover and blend or process until smooth. Stir in the ground spices.
In a large saucepan heat vegetable oil over medium-high heat. Add chile pepper-spice mixture and salt. Bring to boiling; reduce heat. Simmer, uncovered, for 10 minutes. In a small bowl combine the water and masa harina. Stir into the mixture in the saucepan; cook until bubbly.
Meanwhile, in a 5- to 6-quart Dutch oven bring broth to boiling. Add chicken legs; reduce heat. Simmer, covered, for 15 minutes. Add potatoes, chayote, and green beans. Return to boiling; reduce heat. Simmer, covered, for 10 to 15 minutes or until chicken and vegetables are tender.
Using a slotted spoon, transfer chicken and vegetables to a serving platter. Discard broth. Spoon yellow mole over the chicken and vegetables. Sprinkle with cilantro.