Preheat the oven to 400 degrees . In a small bowl, whisk 1/4 cup olive oil, the chopped rosemary and the garlic. Open the lamb like a book; season generously with salt and pepper and rub all over with the rosemary-garlic oil. Roll up the lamb and, using 8 two-foot-long pieces of kitchen twine, tie up the leg, spacing the strings about 2 inches apart.
In a large roasting pan set over two burners, heat 2 tbsp. oil over medium-high. Season the lamb and cook, turning occasionally, until browned all over, about 10 minutes. In a medium bowl, toss the fennel wedges with 2 tbsp. oil; season. Arrange the fennel and the rosemary sprigs around the lamb; roast 30 minutes.
In the same medium bowl, toss the tomatoes, beans and the remaining 2 tbsp. oil; season and add to the roasting pan around the lamb. Stir to combine with the fennel.
Continue roasting the lamb and the vegetables until an instant-read thermometer inserted into the center of the lamb registers 130 degrees for medium, about 30 minutes more. Transfer the lamb to a cutting board; let rest 10 minutes. Transfer the vegetables and their juices to a large, deep platter. Untie and slice the lamb; arrange over the vegetables.