It's wonderful having this hearty, vegetarian soup in the fridge, ready to heat up on a blustery day. Though we love the look of red quinoa here, regular white quinoa can be substituted. Slideshow: More Chowder Recipes
Put the quinoa, water and 1/2 teaspoon salt in a medium saucepan and bring to a boil, then reduce heat to moderately-low and simmer for 10 minutes. Drain the quinoa, saving the liquid. Add enough water to the cooking liquid to make 8 cups.
Meanwhile, heat the olive oil in a large pot over moderate heat and cook the onions and jalapeño, stirring occasionally, until softened, about 10 minutes. Add the garlic and cumin and cook another minute more. Add the sweet potatoes, quinoa and the reserved cooking liquid (and water, if needed) and bring to a boil. Reduce the heat to moderately low and simmer until the sweet potatoes are tender, about 30 minutes. Season to taste with salt and pepper. Stir in the spinach and cook until wilted, about 3 minutes, and serve.
The soup can be made up to 3 days ahead.