1. Pat the chicken breasts dry with paper towels and place them on a cutting board or plate. Season both sides evenly with the salt, black pepper, chili powder, ground cumin, smoked paprika, and garlic powder, pressing the spices onto the surface so they adhere well.

2. Heat the olive oil in a large deep skillet over medium-high heat until the oil is hot and shimmering. Add the seasoned chicken in a single layer without crowding the pan and sear until the first side is deeply golden, then flip and sear the second side. The chicken does not need to be fully cooked through at this point. Transfer the browned chicken to a clean plate and set aside.

3. Reduce the heat under the skillet to medium and add the butter. Once melted, stir in the chopped onion and jalapeño. Cook, stirring often, until the vegetables are softened and fragrant, scraping up any browned bits from the bottom of the pan. Add the minced garlic and cook for about 30 seconds more, just until aromatic.

4. Sprinkle the flour evenly over the sautéed onion and jalapeño and stir to coat them in the fat, forming a thick paste-like mixture. Cook this roux for 1 to 2 minutes, stirring constantly, to remove the raw flour taste and build flavor for the cheese sauce.

5. Slowly pour in the chicken broth while stirring or whisking constantly to avoid lumps, then add the milk or half and half. Bring the mixture to a gentle simmer, stirring frequently, until slightly thickened and smooth. Reduce the heat to low and add the cream cheese, stirring until it melts completely into the sauce.

6. Gradually add the shredded Mexican blend cheese, a handful at a time, stirring between each addition until the cheese is fully melted and the sauce is smooth and velvety. If using diced tomatoes with green chiles, fold them into the sauce now. Taste and adjust the seasoning with a pinch of extra salt or chili powder if needed.

7. Return the seared chicken and any accumulated juices to the skillet, nestling the pieces into the cheese sauce. Simmer gently over low heat for 8 to 10 minutes, or until the chicken is cooked through and reaches an internal temperature of 165°F (74°C), and the sauce has thickened to your liking. Flip the chicken once or twice so it is fully coated in the sauce.

8. Turn off the heat and squeeze the lime juice over the chicken and sauce, then sprinkle with the chopped cilantro. Stir the sauce gently to distribute the lime and herbs.

9. Slice or serve the chicken breasts whole, spooning plenty of the cheese sauce over the top. Serve over cooked rice, with warm tortillas, or alongside roasted vegetables or a simple salad for a complete meal.