In a large stockpot, heat the olive oil over medium-high heat. Add the onion and cook until translucent. Add the rice and cook 1-2 minutes. Add the broth and bring soup to a boil over high heat. Reduce the heat to low and simmer for about 15 minutes, until the rice is tender. Season with salt and pepper, to taste.
In a liquid measuring cup with a spout, whisk together the eggs, lemon zest and juice, and a sprinkle of salt and pepper. Add a ladleful of warm broth into the egg mixture and whisk to temper the eggs. Add 2-3 more ladles of warm broth and whisk the egg mixture.
Meanwhile, add the diced chicken, spinach and parsley to the stockpot and cook until spinach has wilted. Add the egg mixture into the stockpot and stir to combine. Remove pot from the heat and test for seasoning. Serve immediately, with freshly grated Parmesan. Leftovers reheat well. Enjoy!