Add the ground lamb to the pan and cook, breaking up into smaller and smaller pieces, until the meat has lost its pink color. Add the onion back to the pan along with the rice and mix to thoroughly coat rice. Add tomatoes and 1/4 cup water. Cook for 10 minutes or until rice has absorbed juices in the pan. Stir in the allspice, herbs, salt and pepper, mixing well. Set aside, covered, for 10 minutes before stuffing the grape leaves.