Cut off stem from each artichoke; remove bottom leaves, and discard. Trim about 1/2 inch from top of each artichoke. Place artichokes, stem ends down, in a large Dutch oven filled two-thirds with water. Add the garlic halves and lemon slices, and bring to a boil. Cover, reduce heat, and simmer 40 minutes or until a leaf near the center of each artichoke pulls out easily. Remove artichokes from pan, and discard cooking liquid, garlic, and lemon. Remove center leaves and furry thistles with a spoon, and discard. Set artichokes aside.
Combine the bulgur and boiling water in a medium bowl. Cover and let stand for 45 minutes. Drain. Combine the bulgur, tomato, and remaining ingredients in a large bowl.
Spoon 1 cup tabbouleh into center of each artichoke.