In a bowl, mash steamed cauliflower with a potato masher. Stir in onion, flour, garlic, 1/2 tsp. salt, pepper, lemon rind, potatoes, cheese and eggs. Form into 8 patties. Heat a large non-stick skillet over medium-high heat. Add oil; swirl. Cook patties 4 minutes on each side. Combine 1/8 tsp. salt, yogurt and remaining ingredients; serve sauce with fritters.