Melt butter in a small sauté pan over medium heat.
Add onions and garlic and slowly caramelize for 15-20 minutes lowering heat if necessary and stirring occasionally.
Season with salt near the end of cooking and at the last minute add and wilt spinach.
Remove from heat.
Blanch cauliflower in boiling water 3-4 minutes.
Drain and cool.
Whisk together the yogurt and flour.
Stir in the cheese, salt and pepper.
Toss yogurt mixture with cauliflower and caramelized onions and spinach.
Place in baking dish.
Mix together panko, parmesan cheese, oliv oil, and parsley and sprinkle over the top.
Bake 375°for 20 minutes.