Combine the milk and vinegar in a large nonreactive bowl. Add the chicken and marinate at room temperature for about 1 hour, or cover and chill for up to 12 hours.
Preheat the oven to 450 degrees . Line a large rimmed baking sheet with aluminum foil and spray with cooking spray. In a medium bowl, combine the panko with the paprika, oregano, thyme, 11/2 teaspoons salt and 1/2 teaspoon pepper. Remove the chicken pieces from the milk, one at a time, and coat with the crumb mixture. Place the chicken pieces, skin side up, on the prepared baking sheet. Bake until golden brown and cooked through, about 45 minutes.
Meanwhile, melt the butter in a medium saucepan over medium heat. Add the onion and chili powder and cook, stirring occasionally, until the onion is softened, about 4 minutes. Add the corn and jalapeno and cook until warmed through. Stir in the tomatoes and season to taste with salt and pepper.