This grilled-tuna dish makes a quick and healthy meal. The herbed bulghur wheat can be made ahead and set aside while the rest of the ingredients are being prepared.
Bring 2 cups water to a boil. Place bulghur in a large heatproof bowl; cover with the boiling water. Add 1/4 teaspoon salt; stir just to combine, and cover tightly with plastic wrap. Let steam until tender but still slightly chewy, 22 to 25 minutes. If all water has not been absorbed, drain bulghur in a sieve, then return to dried bowl. Let cool. Using a fork, stir in celery leaves, mint, cilantro, and coriander.
Make cherry-tomato salad: In a medium bowl, toss the tomatoes and scallions with the oil, lemon juice, and 1/4 teaspoon salt. Season with pepper. Set aside.
Heat a lightly oiled grill or grill pan over medium-high heat. Sprinkle both sides of each tuna steak with about 1/4 teaspoon salt; season evenly with pepper. Cook until first side is seared with grill marks, 3 to 4 minutes. Flip tuna, and cook 3 minutes more for medium-rare. Serve with herbed bulghur on the side and cherry-tomato salad spooned on top.