Scrub the sweet potatoes and cut off the ends. Place in a large saucepan and cover with water. Sprinkle with 1 tablespoon salt and cover. Bring to a gentle boil and boil for 20 to 30 minutes or until tender. Drain and let stand until the sweet potatoes are cool enough to handle.
Peel the sweet potatoes and cut into cubes in a bowl. Add the black beans, onion and cilantro and toss to mix.
Whisk the mayonnaise, olive oil, Dijon mustard, Worcestershire sauce, red wine vinegar, 1/2 teaspoon salt and pepper in a bowl. Pour over the warm sweet potato mixture and toss to coat.