Cook cauliflower florets in large saucepan of boiling water 5 minutes or until tender-crisp. Drain well.
Meanwhile, mix panko, melted butter, parsley, and 1/2 teaspoon each of the garlic powder and smoked paprika in small bowl. Set aside.
Mix stock, remaining 1 teaspoon each garlic powder and smoked paprika, mustard and sea salt in large saucepan with wire whisk. Bring to boil on high heat. Reduce heat to medium. Add cheeses and cauliflower; cook and stir until cheeses have melted and are smooth, about 5 minutes. Spoon cauliflower mixture into 2-quart baking dish sprayed with no stick cooking spray. Sprinkle panko mixture evenly over top.
Place baking dish on center rack of oven. Broil 2 minutes or until lightly brown on top.