Pat the chicken breasts dry with paper towels. Season evenly with garlic powder, 1 teaspoon Italian seasoning, about 1/2 teaspoon salt per breast, and a few grinds of black pepper. Drizzle with olive oil and rub to coat.

Heat 2 tablespoons olive oil in a large skillet over medium heat. Add the chicken and cook until golden and cooked through, about 6 minutes per side. Transfer to a plate and let rest 10 minutes before slicing.

In the same skillet, melt the butter over medium heat. Add the diced onion and cook, stirring occasionally, until softened, about 3 minutes. Stir in the minced garlic and remaining 1 teaspoon Italian seasoning; cook 1 minute until fragrant.

Add the orzo and stir to coat, cooking for 2 minutes. Pour in the chicken broth and season with a pinch of salt and pepper. Bring to a low boil, then reduce heat to maintain a gentle simmer. Cover and cook until orzo is tender, about 12 minutes.

Uncover the skillet and stir in the baby spinach, heavy cream, and Parmesan cheese. Cook, stirring, until the spinach wilts and the sauce is creamy, about 1 minute.

Remove from heat and stir in the lemon zest and lemon juice. Taste and adjust with more lemon or salt if desired.

Slice the rested chicken into strips. Serve the creamy orzo in bowls, top with sliced chicken, and garnish with lemon slices and chopped parsley.