Prepare a charcoal fire or preheat the grill to medium-high heat.
Pat the steak dry. In a small bowl, combine the rosemary, sage, thyme, black pepper, and kosher salt until well blended. Coat the entire steak with the spice mix and brush with 2 tablespoons of the olive oil. Place on the grill and cook until well-charred, about 12 minutes on the first side and about 9 minutes on the second side. Let stand 5 minutes.
Meanwhile, in a 12 to 14-inch saute pan, heat 1/4 cup olive oil until smoking. Add the garlic and cook until light brown, 3 to 4 minutes. Add the spinach and stir quickly, cooking just until wilted. Remove from the heat, add the lemon juice and salt and pepper, and set aside.
Carve the fillet and strip steaks off the bone and slice. Divide the spinach and steak among 4 plates, giving each some of the fillet, and drizzle each serving with a few tablespoons of the remaining olive oil.