Soak the pozole overnight in water to cover generously, the same amount as you would dried beans. Drain the pozole and place it in a large saucepan with 1 tablespoon of salt and 1 large white onion cut into quarters. Cover with a few inches of water and bring to a simmer. Cover partially and cook until the kernels are tender and have bloomed—this can take anywhere from 75 minutes to 2 hours. Remove from the heat and allow to cool. If there is excess liquid left drain it, but I have never had to drain mine.Meanwhile preheat the broiler and line a sheet pan with foil. Roast the peppers on the pan under the broiler, turning occasionally until blackened and charred all over. Transfer the peppers to a paper bag and seal tight. (You could also place them in a bowl and cover with plastic wrap.) Once the peppers have cooled enough to handle remove and discard the papery skins, seeds and ribs. Transfer the pepper to a blender and set aside.In a large skillet heat a tablespoon of oil over medium high - high heat. Immediately add the remaining white onion wedges, red onion, garlic and tomatillos. Turn the vegetables often, cooking for 8-10 minutes until completely softened and charred. Transfer to the blender with the peppers and puree until smooth.Heat a tablespoon of olive oil in a large soup pot over medium heat. Add the blended tomatillo salsa and season with a generous pinch of salt. Simmer for 10 - 12 minutes. Add the spinach and stir until wilted. Remove from the heat - add the cilantro, oregano and 1 cup of broth. Transfer in batches to a blender or use an immersion blender to blend until smooth. Return to the soup pot and add the remaining 4 cups of broth, the cooked hominy and lime juice.Serve immediately with desired garnishes.