Prepare the Batter: In a mixing bowl, combine flour, cornstarch, baking powder, garlic powder, paprika, and salt. Gradually add cold water while whisking until the batter is smooth and slightly thick.
Heat the Oil: In a deep skillet or pot, heat vegetable oil over medium heat until it reaches 350°F (175°C).
Coat the Mushrooms: Pat the mushrooms dry, then dip them into the batter, ensuring they are evenly coated.
Fry the Mushrooms: Carefully place the battered mushrooms in the hot oil in small batches. Fry for 2-3 minutes or until golden and crispy. Remove with a slotted spoon and place on a paper towel-lined plate to drain excess oil.
Serve: Arrange the fried mushrooms on a platter. Drizzle with sweet chili sauce or serve the sauce on the side for dipping. Garnish with sesame seeds and fresh cilantro if desired.