Pat the chicken dry with a paper towel, then slice it in half horizontally (if not already butterflied). Sprinkle the chicken on both sides with 1 teaspoon of the kosher salt, garlic powder, onion powder, oregano, and a few grinds of black pepper.
Add the olive oil to a large skillet and heat over medium heat. Add the chicken and cook for 3 to 5 minutes per side, until browned on both sides. When the internal temperature is 165°F or the center is no longer pink, remove to a plate.
Place the pan over low heat and melt the butter. Then add the minced garlic and sun dried tomatoes and cook for 30 seconds to 1 minute until the garlic is lightly browned and fragrant. Add the capers, cream, milk, and remaining ¼ teaspoon kosher salt. Simmer for 2 minutes, stirring occasionally and scraping the brown bits off the bottom of the pan.
Add the spinach and cook until wilted, about 1 minute, then return the chicken to the pan and warm it for 2 minutes, spooning the sauce over the chicken. Serve topped with the sauce and grated Parmesan cheese.
