Preheat the oven to 400 degrees.
Season chicken pieces with salt, black pepper, and Italian seasoning.
Heat olive oil in a large oven-safe skillet over medium-high heat. Brown the chicken on both sides, until golden brown, about 3-5 minutes per side. Remove them from the skillet and set aside.
In the same skillet, add butter and diced onion and sauté over medium heat until it becomes translucent. Add minced garlic and cook for an additional 30 seconds.
Whisk in flour for about 1 minute. Pour in the chicken broth slowly, whisking until slightly thickened. Stir in heavy cream and grated Parmesan cheese. Stir well to combine.
Add the gnocchi and baby spinach to the skillet and cook until the spinach has wilted, about 1-2 minutes. Return the browned chicken to the skillet.
Place the skillet in the oven and bake for 10 minutes, or until the top is golden and bubbly.
Remove from the oven, garnish with fresh basil or parsley, and serve immediately.