Preheat the oven to 350 degrees. Generously grease a deep casserole or 13×9-inch baking pan. Set aside
In a large bowl, stir together the cold rice and beaten eggs. Set aside
In a large skillet over medium-high heat, melt the butter. Add the celery, peppers, onions, and spinach and cook, stirring occasionally, until the onions are translucent and the spinach is wilted, about 2 to 3 minutes. Reduce the heat to medium and stir in the artichokes, cream cheese, sour cream, Parmesan, and garlic.
Cook for 5 to 7 minutes, stirring occasionally until the cream cheese has melted and all of the ingredients are well combined. Add the spinach-cheese mixture to the rice. With a wooden spoon, stir in the black pepper, onion powder, garlic powder, and salt.
Pour into the prepared casserole, and cover with foil. Bake for 20 minutes, then remove the foil and bake for an additional 10 minutes, or until the top is nicely browned. Let rest for 15 minutes before serving.