Start by peeling the onions carefully and trimming the ends. Boil them for a few minutes until slightly softened for easier hollowing. Scoop out the center gently, keeping the outer layers intact.
In a bowl, mix cooked quinoa or rice with chopped tomatoes, olives, and garlic. Add feta cheese, herbs, olive oil, salt, pepper, and lemon juice. Stir everything well until the mixture becomes evenly combined and fragrant.
Take each hollowed onion and fill it generously with the prepared mixture. Press lightly so the filling stays in place while baking. Arrange them neatly in a greased baking dish.
Drizzle a little olive oil over the stuffed onions for extra moisture. Cover with foil and bake until the onions become soft and golden. Remove foil in the last minutes for a lightly roasted top.
Let the onions rest slightly before serving to hold their shape better. Sprinkle fresh parsley for a bright finishing touch. Serve warm for the best flavor and texture experience.