Bring a large pot of salted water to a boil. Add the gnocchi and cook according to package instructions until they float to the surface, about 2-3 minutes. Drain and set aside.

In a skillet, heat olive oil over medium heat. Add sliced onions and salt, cooking slowly until they are golden brown and caramelized, about 20-25 minutes. Stir occasionally to prevent burning.

Add the cooked gnocchi to the skillet with caramelized onions. Sprinkle with sugar (if using), black pepper, and half of the Gruyère cheese. Toss gently to combine and heat through.

Transfer to a serving dish and top with remaining Gruyère cheese. Optionally, place under a broiler for 2-3 minutes to melt the cheese. Garnish with chopped parsley before serving.