Cut off the stalks of the squash. Using an apple corer, carefully hollow out the squash and remove the flesh without puncturing the outside of the squash. You can reserve the flesh for another recipe.
Heat the olive oil in a large deep pot over medium heat. Add the onion and ground beef, and season with 7 Spice, salt, and pepper. Cook for 8 minutes, until the beef is browned. Add the uncooked rice and stir to combine. Transfer to a bowl and set aside.
Using a small spoon or your hands, fill the hollowed-out inside of each squash with the rice stuffing. Be sure to leave about ¼ inch of empty space at the top since the rice will expand when cooked. Then stuff a tomato chunk on top to seal the squash and prevent the stuffing from coming out while cooking. Repeat with the remaining squash. If you have any leftover stuffing, you can cook it separately with water.
To make the tomato broth, heat the olive oil in the pot used to cook the beef over medium heat. Add the tomato paste, garlic, salt, and pepper. Cook for 1 minute, or until the mixture becomes fragrant. Add the water and stir to combine.
Transfer the stuffed squash to the deep pot, making sure they're almost entirely submerged in the tomato broth. Add one more cup of water if needed. Bring the mixture to a boil, then lower the heat to a simmer. Place a heatproof plate directly on top of the squash to hold them in place and cook covered for 1 hour and 15 minutes.
Uncover and continue cooking for 15 more minutes, or until the sauce is reduced and the rice is fully cooked.