In fine sieve, rinse quinoa under cold water; drain. In saucepan, bring quinoa, broth and 1 1/2 cups water to boil. Reduce heat; simmer, covered for 15 minutes. Drain in fine sieve; let cool completely in sieve.
Meanwhile, in skillet, heat 1 tablespoons of the oil over medium heat; fry onion, garlic, salt and pepper, stirring occasionally, until onion is softened, about 4 minutes. Add spinach; cook, stirring, until wilted and no liquid remains, about 3 minutes. Let cool; coarsely chop.
LEMON YOGURT SAUCE: Stir together yogurt, onions, lemon juice, salt and pepper. Set aside in refrigerator.
In large bowl, whisk together egg, Parmesan cheese, flour, baking powder and lemon rind; fold in quinoa and spinach mixture. With wet hands, form into 16 cakes; transfer to waxed paper-lined tray. Refrigerate for 1 hour.
In nonstick skillet, heat half of the remaining oil over medium-high heat; fry half of the cakes, turning once with 2 spatulas, until golden brown, about 8 minutes.
Keep warm on baking sheet in 200F oven. Repeat with remaining oil and cakes.
Serve drizzled with Lemon Yogurt Sauce and sprinkled with sesame seeds.