Preheat oven to 475°F In a large bowl, whisk together flour, 1/2 c panko, baking soda and remaining spices. Whisk in lemon juice and club soda. Set aside.
In a small bowl, whisk the egg whites until foamy.
Whisk whites into flour mixture. Using your hands, add cauliflower and combine until all florets are coated. Place remaining panko in a bowl. Lift florets, one at a time out of batter and toss in panko.
Place on a large baking sheet coated with oil. Bake until brown and crispy, about 20 minutes.