Pat the chicken breasts dry with paper towels and butterfly each one. To butterfly chicken, place a chicken breast on a cutting board and press your hand flat on top. Using a sharp knife, slice horizontally through the thicker side, stopping before you cut all the way through. Repeat with the remaining chicken breasts.
Season the butterflied chicken evenly on all sides with garlic powder, paprika, salt, and black pepper.
In a medium bowl, combine the cream cheese, ½ cup of the cheddar cheese, ¼ cup of the Monterey Jack cheese, and the finely diced jalapeños. Stir until well-mixed.
Divide the filling evenly, placing about ¼ cup in the center of each butterflied chicken breast. Fold each chicken breast closed and secure with toothpicks as needed to hold the filling inside.
To a large oven-safe skillet over medium heat, add olive oil and butter. Once the oil is hot and the butter has melted, add the stuffed chicken breasts. Cook for about 8 minutes. Then, flip the stuffed chicken breasts and cook for an additional 12-15 minutes, or until the chicken reaches an internal temperature of 165°F. (After flipping the chicken breasts, I covered the skillet with aluminum foil to help trap heat and steam, ensuring the chicken cooks through without drying out.)
Remove the chicken from the pan, place it on a plate, and tent with aluminum foil to keep warm.
Preheat the broiler.
In the same skillet over medium heat, melt butter. Add the onion and cook for 3-5 minutes, or until softened and lightly browned. Add garlic and cook for 1 more minute.
Add the thawed corn, heavy cream, salt, black pepper, and crushed red pepper flakes to the skillet. Stir to combine.
In a small bowl, whisk together the milk and flour until smooth. Pour the milk mixture into the corn, stirring continuously until the mixture thickens, about 2 minutes.
Add the Parmesan cheese to the skillet, stirring until melted and fully incorporated.
Nestle the cooked, stuffed chicken breasts back into the skillet with the creamed corn. Sprinkle each chicken breast with the remaining cheddar and Monterey Jack cheese, and top with the sliced jalapeño.
Place the skillet under the broiler for 1-2 minutes, or until the cheese on top is melted and bubbly.