In a bowl, combine salt, pepper, garlic powder, onion powder, and smoked paprika; toss the chicken pieces to coat evenly.
Heat the olive oil in a large 12-inch skillet over medium-high heat.
Add the seasoned chicken and cook, stirring occasionally, until golden and cooked through, about 5–7 minutes; transfer the chicken to a plate and set aside.
Reduce heat to medium and melt 2 tablespoons of the butter in the same skillet.
Add the minced garlic and sauté until fragrant, about 1 minute.
Pour in the chicken broth and scrape up any browned bits from the bottom of the skillet; bring to a boil and reduce for 2–3 minutes.
Lower the heat to medium, then stir in the heavy cream, lemon juice and zest, dried oregano, and red pepper flakes; simmer until the sauce begins to thicken, about 5 minutes.
Whisk in the remaining 2 tablespoons of butter until melted, then add the chopped spinach and cook until wilted.
Return the chicken to the skillet, coat it with the sauce, and simmer 2–3 minutes until heated through.
Serve topped with freshly grated Parmesan if desired.