In a small bowl, whisk together lemon juice and mustard, then slowly whisk in the olive oil. Stir in chives and season with salt and pepper.
In a large bowl, gently toss sliced celery, butter beans and capers. Add lemon-mustard vinaigrette and toss to coat salad. Refrigerate.
Meanwhile, in a large skillet, heat vegetable oil over medium heat. Place House-Autry Medium Hot Breader on a piece of waxed paper. Dredge tuna steaks in breader until top and bottom are well coated. Sear tuna on both sides until golden brown, about 4 minutes. (Tuna will be medium rare. If you want your tuna to be less rare, cook about 4 minutes longer. Cooking times will vary depending on thickness of tuna.) Remove from pan and let sit for 2 minutes. Slice tuna. Divide salad among 4 bowls and top with tuna.
Serve immediately.
