Slice the chicken breasts lengthwise into strips about 2 inches wide, then pound each piece to about 3/4–1 inch thick. Pat dry with paper towels.
Season both sides of the chicken with sea salt, black pepper, Italian seasoning, onion powder, and paprika.
Heat a large skillet over medium-high heat and melt 2 tablespoons of the butter. Add the minced garlic and cook, stirring, for about 1 minute until fragrant.
Add the seasoned chicken to the hot skillet and sear without moving for about 2 minutes per side until golden; it will not be fully cooked. Remove chicken to a plate and set aside.
Add the remaining 1 tablespoon butter to the skillet, then add the long-grain rice and toast, stirring, for 1–2 minutes so it is slightly browned but not burnt.
Pour in the chicken broth and add the chopped spinach; stir to combine and bring the mixture to a gentle boil.
Once boiling, reduce heat to low (a low simmer), return the chicken to the pan by laying it on top of the rice (not fully submerged), cover, and cook for 15–20 minutes until the rice has absorbed the liquid and the chicken reaches 165°F internally.
When cooked, push the chicken to the side, sprinkle the grated Parmesan over the rice, and stir to melt and combine. Serve with extra Parmesan and chopped parsley if desired.