Pick the parsley leaves off the stems (you should have about 6 cups lightly packed). Wash and spin-dry in a salad spinner, then lay out on paper towels and pat dry. Leave to air-dry for at least 30 minutes, if possible, then finely chop.
Spread the cannellini beans on new paper towels, cover with more paper towels, and gently pat dry.
Combine the parsley, beans, tomatoes, scallions, mint, lemon juice, olive oil, garlic, salt, and pepper in a medium bowl and gently toss to combine. Taste and add more salt if needed. Serve immediately.