Make the salsa verde: Pulse the parsley, scallions, capers, lemon zest and juice, anchovies, garlic, mustard and olive oil in a food processor until slightly chunky. Pour into a bowl and season with salt.
Preheat a grill to high or place a grill pan over high heat. Pierce the steak all over with a fork and season with salt and pepper. Oil the grill or pan; grill the steak, 4 to 5 minutes per side for medium-rare, turning once. Transfer to a cutting board and let rest for 5 minutes.
Slice the tomatoes and season with salt and pepper. Thinly slice the steak against the grain. Serve with the tomatoes and salsa verde.
Photograph by Antonis Achilleos
Recipe courtesy Food Network Magazine