Fill large saucepan with water. Bring to a boil then reduce heat to low. Add chicken legs. Cover and simmer 20 to 25 min., or until cooked through. Remove chicken from poaching liquid, reserving the liquid. Cool chicken. Remove skin and discard. Remove meat from bones. Discard bones. Chop meat into bite-sized pieces.
Meanwhile, bring poaching liquid back to a boil. Add pasta and cook 7 to 8 min., or until tender. Add asparagus and cook 1 min., or until tender-crisp. Drain.
Toss pasta and asparagus with parsley, oil, lemon juice, mint, garlic and salt. Mix in chicken, tomatoes and onion.