Bring a pot of lightly salted water to a boil over high heat. Add the quinoa, and cook until the quinoa is tender, 15 to 20 minutes. Drain in a mesh strainer, and rinse until cold; set aside.
Heat the olive oil in a skillet over medium heat, stir in the sunflower seeds, and cook until lightly toasted, about 2 minutes. Stir in the garlic, and cook until the garlic softens and the aroma mellows, about 2 minutes. Stir in the cooled quinoa and spinach; cook and stir until the quinoa is hot, and the spinach has wilted. Stir in the lemon juice, and all but a pinch of the cheese. Stir until the cheese has melted. Serve sprinkled with the remaining cheese.