How to Make It
In a small bowl, combine the white and black sesame seeds with the lime zest, lemongrass, paprika, Aleppo pepper, black pepper and salt. Lightly brush the tuna with oil and sprinkle the sesame mixture all over it, pressing to help the crust adhere.
Heat 2 tablespoons of vegetable oil in each of 2 large nonstick skillets until the oil is almost smoking. Add the crusted tuna steaks and cook them over moderately high heat until they are slightly pink in the center, about 2 minutes per side. Transfer the crusted tuna steaks to plates and serve them with lime wedges and mayonnaise.