Marinate the chicken wings: Sprinkle chicken all over with salt and pepper. Transfer chicken to a large ziplock plastic bag. Add onion, garlic, soy sauce, vinegar, oil, and bay leaves. Seal bag and toss mixture to evenly combine. Marinate chicken mixture in refrigerator at least 8 hours or up to 1 day.
Prepare for roasting: Preheat oven to 425°F. Line a rimmed baking sheet with aluminum foil. Lightly coat an oven-safe wire rack with cooking spray and set in baking sheet.
Arrange wings for roasting: Remove chicken wings from marinade, scraping off excess, and transfer to a paper towel–lined plate; pat dry. Reserve marinade in bag. Arrange wings at least ¼ inch apart on prepared wire rack.
Roast the wings: Roast in preheated oven until browned and crisp and a thermometer inserted in thickest portion of meat registers at least 165°F, 45 to 50 minutes, flipping wings after 25 minutes.
Reduce the marinade: Meanwhile, bring reserved marinade to a boil in a small saucepan over medium heat. Boil, stirring occasionally, until liquid is slightly thickened and reduced to about 3 tablespoons, 14 to 16 minutes. Pour mixture through a fine wire-mesh strainer set over a large bowl; discard solids. Set reduced marinade aside.
Make the Filipino pico: Reserve 1 tablespoon scallions, 1 tablespoon cilantro, and a few slices of serrano for garnish. Stir together tomatoes and remaining scallions, cilantro, and serrano in a medium bowl. Stir in fish sauce and season to taste with salt. Set aside.
Finish the wings: Add roasted chicken wings to bowl with reduced marinade and toss to coat. Transfer to a platter and garnish with reserved scallions, cilantro, and serrano. Sprinkle evenly with fried garlic.
Serve: Serve immediately alongside Filipino pico and white rice.