Grind porcini mushrooms to a powder in a coffee grinder or a blender. Transfer to a bowl and add all other ingredients. Stir until fully combined and mixture is a paste.
Brush the steaks on both sides with the porcini paste. Cover and refrigerate for at least 30 minutes.
Prepare a medium-hot fire in your grill. Grill the steaks, covered, for 3 to 4 minutes on each side for medium-rare.