In a large deep sauté pan or pot heat the oil on medium-high and saute the onions until tender and wilted, about 6 minutes. Drop the heat to medium, add the frozen spinach, dill, coriander, cayenne pepper, and water, and stir. Cook the spinach for 20 minutes, stirring regularly. If the pan dries out, add more water, a tablespoon or 2 at a time. Add the cilantro, black pepper, salt, and lemon juice. Stir and continue to cook another 10 minutes until the spinach is dark and the texture is sort of creamy.