Preheat the oven to 400 degrees F. Cut the tops off each pepper, reserve them and hollow out the insides of the peppers of any seeds and seed walls. Sprinkle the insides with a pinch salt and a pinch pepper and set aside.
Heat 1 teaspoon of the oil in a large nonstick skillet over medium heat and add the garlic and onions. Cook until softened, 3 minutes, and then add the beef, oregano, cinnamon and cumin. Cook, breaking up the meat with a wooden spoon, until no longer pink. Stir in 1 tablespoon of the tomato paste until it coats the meat and is slightly darkened. Stir in the broth, rice and lentils. Remove from the heat and set aside until the liquid is absorbed and the mixture is cooled slightly. Season with 1/2 teaspoon salt and 1/4 teaspoon pepper.
Divide the filling among the peppers and place the tops back on. Set the peppers upright in a small baking dish, such as an 8-inch square baking dish. Whisk 1 1/2 cups water with the remaining tablespoon of tomato paste and olive oil. Pour into the dish around the peppers. Cover tightly with foil and bake until the peppers are tender and the rice and lentils are cooked through, about 1 hour 15 minutes.
Carefully transfer the peppers to a serving dish and pour the cooking liquid into a medium nonstick skillet. Boil over high heat until the sauce is thickened and reduced to about 1/2 cup. Remove from the heat and add the dill. Season with salt and pepper. Serve the sauce with the stuffed peppers.