In a bowl, combine flour, cornstarch, and baking powder. In a separate bowl, whisk together the egg, cold sparkling water, and soy sauce. Gradually mix the wet ingredients into the dry ingredients until smooth.
Heat 2-3 inches of vegetable oil in a deep pot over medium-high heat. Dip the chicken slices into the tempura batter, letting any excess drip off. Fry in batches for 3–4 minutes until golden and crispy. Transfer to a plate lined with paper towels to drain excess oil.
In a large bowl, mix cooked sushi rice with rice vinegar and sugar (optional) for added flavor. Divide the rice evenly into four bowls.
Arrange the mango, carrot, pickled onion, and broccoli around the rice in each bowl. Place 3–4 pieces of chicken tempura in the center.
In a small bowl, whisk together soy sauce, sesame oil, honey, and rice vinegar. Drizzle the sauce over the poke bowls or serve on the side.
Garnish with sesame seeds. Serve immediately and enjoy.