1In a small bowl, combine red onion, lemon juice, pepper, and salt. Whisk in olive oil; set aside.
2In a large bowl, slightly mash beans. Add tuna, tomatoes, and parsley. Pour dressing over bean mixture; stir gently.
3Divide bean mixture among tortillas. Top with carrot. Roll up tightly. Serve immediately, or cover and chill for up to 6 hours.