1. Position a rack in the upper third of the oven and preheat to 350°F. Oil a 13- by 9-inch heavy metal, ceramic, or glass baking dish and set aside.
2. Put the rice and 1 tablespoon of the salt in a medium saucepan, cover with cold water by 2 inches, and bring to a simmer over medium heat. Cook approximately 30 minutes, until the rice is still a little chewy. Drain and reserve.
3. While the rice is cooking, put the olive oil in a medium heavy-based saucepan and set over medium heat. Add the onion, and gently sauté until translucent, 5 to 7 minutes. Cut a good slice off the tomatoes at the stalk end for the lid and shave a little slice off the base so the tomatoes stand straight; set each top next to its tomato.
4. Use a teaspoon to scoop the pulp out into a small bowl, chop the pulp, and add it to the onions along with the accumulated tomato juices and the remaining teaspoon salt, the garlic, oregano, and pepper. Cook briskly for 5 minutes.
5. Add the rice and stir for 3 minutes, or until most of the liquid is absorbed; set aside to cool. Stir in the pine nuts, then fill the tomatoes (making sure not to pack down too tightly), piling the mixture over the rim. Press each tomato lid down on top, and place the stuffed tomatoes 1 inch apart in the baking dish. If there is any extra rice mixture, spoon it around the tomatoes. The dish can be brought to this point the day before, covered, and refrigerated. When you're ready to bake the tomatoes, drizzle with a little extra olive oil and bake for 45 minutes to 1 hour, depending on the size of the tomatoes, adding 10 minutes if they are cold from the fridge.
6. These look most authentic if the tomato skin is slightly blackened on the top. If necessary, turn the oven up to 450°F for the last 5 to 10 minutes. The good news is that these tomatoes are just as katapliktiko (unspeakably fabulous) warm or at room temperature, so you could bake them earlier in the day if you need space in the oven. Cover with plastic wrap while the tomatoes are still just a little warm. The condensation that forms will keep them from drying out.
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