Bring a large pot of salted water to a boil. Add the broccoli rabe and cook for 2 minutes. Drain and set aside.

In a large skillet, heat the olive oil over medium heat. Add the minced garlic and red pepper flakes. Cook for 1 minute until fragrant.

Add the drained broccoli rabe to the skillet and sauté for 5-7 minutes, until tender.

Add the sardines to the skillet and cook for an additional 2-3 minutes, until heated through.

Season with salt and pepper to taste. Serve hot, topped with grated Parmesan cheese if desired.