Toss the garlic, chopped rosemary, 1 tablespoon salt and the red pepper flakes in a small bowl. Make 3/4-inch-deep cuts between the rib bones of the pork. Stuff some of the garlic mixture into each cut. Rub the lemon halves over the pork, then rub with the remaining garlic mixture. Cover with plastic wrap and refrigerate overnight.
Bring the pork to room temperature, about 30 minutes. Position a rack in the upper third of the oven and preheat to 375 degrees F. Cut each fennel bulb in half, then cut each half into wedges. Scatter the fennel and rosemary sprigs in a medium roasting pan (it's best if the roast fits snugly in the pan). Place the pork in the roasting pan on top of the fennel, fat side up, and roast until a thermometer inserted into the center of the pork registers 145 degrees F, about 1 hour, 45 minutes. Transfer the pork to a platter or cutting board and cover loosely with foil; let rest 15 minutes.
Meanwhile, turn the fennel wedges and return the pan to the oven. Continue roasting until the fennel is caramelized, about 15 minutes. Cut the pork into chops and serve with the fennel.