Bring 2 to 3 cups of water to a boil in a small pot and blanch the garlic cloves for 3 to 4 minutes; drain. Heat 1 tb. of the oil in a small skillet over medium heat and brown the garlic until golden all over.
Cut the leaf stalks and the hard butt ends from the fennel bulbs, leaving just the bulbous stem, a piece 2.5 to 9 cm long. Halve the small bulbs lengthwise; quarter the larger bulbs. In a large skillet, heat the remaining oil and the water over medium heat. Add the fennel in a single layer and the rosemary. (If you have more fennel than your skillet can accommodate in a single layer, save half the oil and rosemary to cook with half the fennel in a second batch.) Cover and cook the fennel, turning once or twice, until water cooks away and the fennel is tender and browning, about 15 minutes. If the fennel begins to brown before it feels tender, add a little more water; if it becomes tender before browning, raise the heat or take off the lid to speed browning.
When the fennel is tender and browned, add the garlic and olives to warm through. Season to taste with salt and pepper. Garnish with lemon slices.