Creating Greek Stuffed Onions (Salantourmasi) is straightforward if you follow these steps:

1. Preheat the Oven: Set your oven to 350°F (175°C).

2. Prepare the Onions: Peel the sweet onions and remove the center layers carefully to create bowls, leaving the outer layers intact. Reserve the inner layers for the filling.

3. Sauté Filling Ingredients: In a skillet over medium heat, heat olive oil. Add the chopped onion, garlic, and sauté until translucent. Stir in the ground meat, cooking until browned.

4. Add Rice and Tomatoes: Mix in the rice, chopped tomatoes, oregano, cinnamon, salt, and pepper. Cook for a few minutes until flavors meld.

5. Stuff the Onions: Fill each onion with the meat and rice mixture, pressing down gently to pack it in.

6. Place in Baking Dish: Arrange the stuffed onions upright in a baking dish. Pour water or broth around the onions to keep them moist during cooking.

7. Bake: Cover the dish with aluminum foil and bake for about 1 hour. Remove the foil and allow the onions to brown lightly for an additional 15 minutes.

8. Check for Doneness: The onions should be tender and the filling well-cooked. A fork should easily pierce through the onions.

9. Serve: Remove from the oven and let cool slightly before serving.

These steps will guide you in creating these incredible stuffed onions with ease.