It’ll be slightly different, but yes! Just thaw it completely first and squeeze out as much liquid as possible, since frozen spinach holds a lot of water. Because it’s already blanched before freezing, it will cook much faster than fresh spinach, so just sauté the garlic in olive oil, then add the spinach and cook for a few minutes until heated through. The texture will be a bit softer than fresh spinach, but it’s still delicious. Enjoy!