Coarsely chop the rosemary, thyme and scallions. Transfer to a small bowl and mix with 1 tablespoon olive oil.
Season the tuna all over with salt and pepper and put in a shallow dish. Coat with the herb mixture on both sides; cover and refrigerate 1 to 4 hours.
Heat the remaining 2 tablespoons olive oil in a large skillet over high heat. Add the tuna and sear until golden, 2 to 3 minutes per side for medium rare.
Transfer to a cutting board and let rest 5 minutes before slicing.
Photograph by Anna Williams
Recipe courtesy Food Network Magazine