Cut the top off the garlic head. Drizzle it with about 1 tablespoon olive oil, season with salt and pepper, to taste, and wrap in aluminum foil. Roast in the oven for 30 minutes, then remove and let cool.
Once cool, squeeze the roasted garlic cloves from the skin into a small bowl. Add the 3 tablespoons of olive oil, the red pepper flakes, and fresh herbs. Adjust the seasoning with salt and pepper, if necessary. Mix well to make a paste.
Season the lamb racks with salt and pepper, then rub the garlic-herb mixture evenly into the meat.
Preheat a grill to medium-high heat. (see Cook's Note)
Grill the lamb racks, meat side down, for about 3 minutes on the first side. Turn, then let the second side grill for 5 minutes total, for medium-rare doneness. Cook slightly longer for medium. (see Cook's Note)
Transfer the lamb from the grill to a platter and tent the racks with foil. Let them rest for 10 minutes before slicing between each rib to separate the chops.
Test by holding your hand 5 inches above the grates. If your hand cannot stand the heat after 3 to 4 seconds, the grill is ready. Let the lamb reach 125 degrees F on an instant-read thermometer, for medium-rare doneness or 130 degrees F for medium.