Place quinoa in a medium-sized saucepan and cook dry, while stirring, over medium heat until the quinoa has a nutty aroma and begins to pop slightly. When the quinoa has toasted, add 6 cups of water; bring to a boil over high heat. Lower heat to medium and simmer for 20 minutes. Drain in a colander and reserve. Heat oil in a saucepan over medium heat. Add onion and sauté until soft, about 4 minutes. Stir in cumin and sauté briefly. Add half the crumbled cheese and cook, stirring, for 30 seconds. Add salt, potatoes, 1-1/4 cups water, and 3 cups milk; simmer until the potatoes are soft, about 20 minutes. Stir in the quinoa and the ground peanuts. Add remaining cheese and stir to mix for 2 to 5 minutes. Thin with more milk if the soup is too thick. Adjust seasoning with lime juice to taste and garnish with serrano pepper and cilantro. Makes 4 servings.