In a medium cast-iron skillet coated with cooking spray, cook yellow onion over medium heat, stirring, 5 minutes. Add kale, garlic and mushroom; stir 5 minutes. Add sweet potatoes. Whisk eggs, egg whites, 2 tbsp. water and paprika in a bowl; stir into kale-potato mixture. Cook over medium-low heat 1 minute. Transfer skillet to oven; bake until eggs are set and center is slightly runny, 8 – 10 minutes. Broil until top is golden, 1 minute.