Heat olive oil in a large stock pot or Dutch oven. Add onions and cook until they’re translucent.
Add mushrooms and saute for another 3-4 minutes before adding garlic. Stir and continue to cook for 1 more minute.
Add broth and bay leaves. Bring to a boil, then add the rice. Season with kosher salt and pepper. Lower heat to simmering and let cook for 20 minutes.
Place eggs, lemon juice and zest in a blender and quickly blend to combine.
While the blender is running, stream in 1 cup of the hot soup with rice and blend for 30 seconds.
Remove the stock pot from the heat and pour the blender contents into the soup, stirring constantly.
Finally, stir in chicken and spinach and mix until spinach has wilted. Serve in bowls.