How you do it:

1. Heat grill.
2. In a bowl, combine tomato, onion, jalapeño, lime and cilantro. Season with salt and pepper. Set aside.
3. Brush tuna with oil.
4. Grill fish about 5 minutes per side until fish flakes easily with a fork. 
5. Remove from grill and set aside.
6. Heat beans in a saucepan over medium heat.
7. Meanwhile, place tortillas on grill for 15 seconds per side.
8. Cut tuna into 1-inch chunks.
9. In a bowl, combine tuna with tomato mixture and avocado sprinkled with any remaining lime juice. 
10. Layer each warm tortilla with ¼ cup black beans and a portion of tuna salad.