Arrange two oven racks in the upper middle and lower middle positions, respectively. Preheat oven to 250 degrees. Line a baking sheet with foil and place a wire rack on top. Coat rack with nonstick spray.
Pat wings dry with paper towels. In a large zipper-top plastic bag, add baking powder and wings and toss to coat.
Arrange coated wings skin-side up on rack. Bake for 30 minutes on lower-middle oven rack.
Increase oven temperature to 425 degrees and transfer baking sheet to upper-middle rack. Bake an additional 45 to 50 minutes, until the wings are golden brown and crispy.
Meanwhile, in a 3-quart saucepan or deep skillet, heat oil until shimmering. Add bacon and onions and fry until the onions have softened, about 5 minutes.
Stir in garlic until fragrant, about 30 seconds. Whisk in Coca-Cola, scraping up any browned bits from the bottom of the pan.
Stir in brown sugar and soy sauce. Transfer 2 tablespoons Coca-Cola sauce to a small bowl and whisk in cornstarch until smooth.
Add back to pan and bring to a boil. Reduce heat and simmer until thickened and reduced by half, about 20 minutes. Strain through a fine-mesh sieve, pushing down on the solids to extract as much liquid as possible. Keep warm on stove until wings have finished baking.
Toss the crispy wings with Coca-Cola sauce and serve.