1. In a 6- to 8-quart pan over high heat, bring 2 quarts water to a boil. Add pasta; cook until tender to bite, 9 to 11 minutes. Drain; immerse in cold water. When pasta is cool, in about 3 minutes, drain and pour into a large bowl.
2. Meanwhile, in a 10- to 12-inch frying pan over high heat, stir onions in oil until limp and slightly browned, about 5 minutes. Add to pasta along with beans, shrimp, cherry tomatoes, broth, lemon juice, mint, and parsley. Mix and add salt to taste.