Bring chicken stock to simmer over medium heat. Stir in rice and chicken shreds. Season to taste with salt and pepper and bring back to the simmer. Add sliced mushrooms and simmer 3 minutes. Add scallions and simmer 1 minute. Whisk together egg yolk and lime juice in small bowl. Ladle some hot soup into bowl containing egg yolk mixture while whisking constantly. Stir this tempered egg mixture into pot and simmer 1 more minute until soup thickens. Serve immediately.
Put chicken stock in small saucepan and bring to a simmer over medium heat. Season with salt & pepper to taste. Stir in corn and onion and cook 1 minute. Stir in chicken shreds and bring back to boil. Add lime juice and remove from heat. Divide avocado, tomato and cilantro between 2 soup bowls. Ladle stock over, dividing solids equally. Garnish with tortilla chips and enjoy.
c.1997, M.S. Milliken & S. Feniger, all rights reserved