In a tall narrow stockpot, bring the ginger, lemongrass, chilies, lime zest, and stock to a boil. Lower the heat and simmer for 10 minutes. Remove from the heat and cool. Season with the salt.
Mash the egg whites and shells, the ground meat, and the tomato together. Whisk this into the cooled broth. Slowly bring the mixture to a boil, stirring frequently with a wooden spoon. As the liqu