Preheat your oven to 450°F. While it heats, finely chop the large onion, mince the 5 garlic cloves, and finely dice the 1.5 bell peppers for the filling. Wash the 10 whole bell peppers thoroughly, then carefully cut off the tops and scoop out all seeds and membranes with a small spoon, being careful not to puncture the sides. Set the hollowed peppers aside on a clean surface. Having everything prepped before you start cooking ensures a smooth workflow.
In a large mixing bowl, combine the 2.25 cups rice with the chopped onion, minced garlic, diced pepper, 4 tbsp tomato sauce, 2.5 tbsp pomegranate molasses, 2.5 tsp salt, 1.5 tsp seven spice, 0.75 tsp cinnamon, and 0.75 tsp black pepper. Mix everything together until the rice and seasonings are evenly distributed throughout. The rice will absorb the flavors during cooking and create a deeply seasoned filling.
Heat 3 tbsp olive oil in a large skillet over medium heat. Once shimmering, add the rice filling mixture and sauté for 3-4 minutes, stirring occasionally. This light toasting brings out the spices and begins the flavor development. Transfer the mixture to a bowl to cool slightly, then carefully stuff each hollowed pepper about three-quarters full, leaving some space at the top for rice expansion during cooking. I find that not overstuffing prevents the peppers from bursting and allows the rice to cook evenly.
Arrange the stuffed peppers upright in a 9x13 inch baking dish (or similar size that fits them snugly). In a separate bowl, whisk together 1.25 cups tomato sauce, 3.5 cups water, the crumbled stock cube, 0.75 tsp salt, 1 tbsp pomegranate molasses, 2 tbsp olive oil, and 0.5 tsp sugar. This sauce base will braise the peppers and keep them moist while the rice cooks through.
Pour the braising liquid evenly around the peppers, then cover the baking dish tightly with foil. Bake for 35 minutes at 450°F to allow the rice to absorb liquid and cook through. Remove the foil, gently baste each pepper with the liquid in the bottom of the dish, then cover again and bake for 10 more minutes. Uncover one final time and bake for 5 minutes to allow the tops of the peppers to slightly caramelize. The initial covered time steams the peppers gently, while the final uncovered minutes add a touch of color and texture.
Remove the peppers from the oven and let them rest for 5 minutes before serving. Garnish generously with fresh parsley. Serve the peppers in shallow bowls with some of the braising liquid spooned over and around them for an authentic presentation.