Begin by placing your boneless, skinless chicken breasts between two sheets of plastic wrap. Using a meat mallet or rolling pin, pound the chicken to an even thickness of about ¾ to 1 inch.

In a small bowl, combine chili powder, cumin, garlic powder, onion powder, oregano, salt, and black pepper. Pat the chicken dry, drizzle it with olive oil, and generously season both sides with the spice mixture.

Heat a large skillet over medium-high heat and add a splash of olive oil. Carefully place the seasoned chicken breasts into the skillet. Sear for 4-6 minutes on each side until golden brown and an internal temperature of 165°F (74°C) is reached.

In the same skillet, add more olive oil if needed and toss in diced yellow onion and bell pepper. Sauté for about 7-10 minutes until soft and slightly caramelized.

Stir in the minced garlic and a pinch of chili powder. Cook for an additional 1-2 minutes until fragrant, then remove from the skillet and set aside.

In the same skillet, add unsalted butter and allow it to melt over medium heat. Whisk in all-purpose flour, stirring constantly for 1-2 minutes to form a roux.

Slowly whisk in warmed whole milk, stirring for about 3-5 minutes until thickened and bubbly.

Reduce the heat to low, and add Monterey Jack, sharp cheddar, and Oaxaca/Queso Blanco cheeses one handful at a time. Stir until fully melted and smooth.

Mix in chopped pickled jalapeños and their brine, cumin, and cayenne pepper according to your spice preference. Taste and adjust seasoning as needed.

In an oven-safe skillet or a baking dish, layer half of the sautéed vegetables, place the seared chicken on top, cover with the remaining vegetables, and pour the creamy cheese sauce over the dish.

Preheat your oven to 375°F (190°C) and bake for 10-15 minutes until bubbly and hot throughout. Broil for an extra minute or two if a crispy top is desired.

Let the dish rest for a few minutes before garnishing with fresh cilantro and serving with lime wedges, tortilla chips, warm tortillas, or cooked rice.