In a large soup pot, bring chicken broth to a boil. Add rice, salt and pepper and simmer until rice is tender, about 15 minutes.
Remove one cup of the broth from the pot and pour into a medium bowl. Add corn starch and whisk until dissolved. Pour in lemon juice and whisk once more.
To temper the eggs, slowly add the whisked eggs to the broth/cornstarch/lemon juice mixture. Whisk constantly so that the eggs gradually come to temperature. Continue until all of the eggs are fully incorporated.
Pour the warmed egg/broth mixture back into the large soup pot and stir until mixture begins to thicken, about 5 minutes.
Add shredded chicken breasts and cook until heated through. Check for seasoning and adjust accordingly. Serve with sliced scallions if you wish.
Notes
This soup is great with or without shredded chicken. I also love freezing it for busy weeknight dinners when I'm low on groceries.