In a kettle cook the scallion in the butter over moderately low heat, stirring, until it is softened, add the bulgur and the zest, and cook the mixture, stirring, for 1 minute. Add the broth, bring to a boil, and simmer the mixture, covered, for 10 minutes, or until the liquid is absorbed. Fluff the bulgur with a fork, stir in the sliced chives, and let the mixture stand, covered, off the heat for 5 minutes. Season the bulgur mixture with salt and pepper. Using an oiled 2/3 cup timbale mold and forming 1 timbale at a time, pack the bulgur mixture into the mold and invert it onto dinner plates. Garnish the timbales with the chive blades and the lemon slices.