Preheat oven to 425°.
Leave root and 1 inch stem on beets; scrub with a brush. Wrap each beet in foil. Place on a baking sheet. Bake at 425° for 45 minutes or until tender. Cool. Trim off roots and stems; rub off skin. Cut beets into 1/2-inch slices. Cut each slice into quarters. Combine beets, 1 teaspoon vinegar, oil, 1/4 teaspoon pepper, and 1/8 teaspoon salt.
Combine 4 teaspoons vinegar, 1/8 teaspoon salt, 1/4 teaspoon pepper, onion, and juice; let stand 30 minutes. Stir in jicama and tangerine.
Arrange 1/2 cup watercress on each of 4 plates. Mound 3/4 cup beet mixture in center of each plate. Arrange 3/4 cup jicama mixture around beets. Serve immediately.