Combine first 5 ingredients in a large saucepan, and bring to a boil. Reduce heat, and simmer 15 minutes. Remove potatoes with a slotted spoon. Bring broth mixture to a boil; cook until reduced to 1/2 cup (about 8 minutes). Combine broth mixture, potatoes, and 1/4 teaspoon salt in a bowl; set aside.
Steam the peas, covered, 2 minutes or until crisp-tender. Rinse peas with cold water, and drain. Steam asparagus, covered, for 2 minutes or until crisp-tender. Rinse asparagus with cold water; drain. Steam the carrots, covered, 4 minutes or until crisp-tender. Rinse carrots with cold water; drain. Combine 1/4 teaspoon salt, peas, asparagus, carrots, oil, rind, and pepper in a large bowl. Combine potato mixture, vegetable mixture, radishes, mint, cilantro, and parsley, tossing well to coat. Arrange the watercress on each of 8 plates; divide the potato mixture evenly among plates.