Prepare the Bell Peppers.

Wash and dry the 4 bell peppers: Slice each pepper in half lengthwise through the stem area, then remove the seeds and white membranes. Trim away any hard stem pieces while keeping the pepper halves intact. Brush the outside of each half lightly with the 1 tablespoon (15 mL) olive oil. Set them cut-side up in the 9 x 13-inch (23 x 33 cm) metal pan. The peppers should sit upright without tipping.

Preheat the Grill.

Preheat the grill to 375°F (190°C), allowing approximately 10 to 15 minutes for heating while you prepare the filling. Arrange the grill for indirect cooking, with a burner turned off or a charcoal-free area beneath the pan. Close the lid and allow the temperature to stabilize. The grill should maintain steady heat without direct flames beneath the peppers.

Cook the Ground Beef.

Place the 12-inch (30 cm) skillet over medium heat. Add the 1 pound (454 g) ground beef and the diced onion. Cook for approximately 7 to 9 minutes, breaking the beef into small pieces with a wooden spoon. Stir occasionally until the onion is softened and the beef is browned and reaches an internal temperature of 160°F (71°C). If excess fat collects in the skillet, carefully drain it before continuing.

Add the Seasonings.

Add the 2 minced garlic cloves, 1 teaspoon (3 g) chili powder, 1 teaspoon (2 g) cumin, 1 teaspoon (6 g) salt, and ½ teaspoon (1 g) black pepper to the skillet. Stir over medium heat for 30 to 60 seconds, until the garlic is fragrant but not browned. Keep the mixture moving so the spices don't scorch.

Combine the Filling.

Add the 1 cup (240 g) diced tomatoes with their juices and 2 tablespoons (30 g) tomato paste. Stir for approximately 1 minute over medium heat until the tomato paste is evenly distributed. Remove the skillet from the heat, then fold in the 1½ cups (240 g) cooked white rice. Transfer the mixture to the medium mixing bowl if needed for easier handling. The filling should look moist and evenly combined, without excess liquid pooling at the bottom.

Stuff the Pepper Halves.

Divide the prepared beef and rice mixture evenly among the 8 bell pepper halves. Spoon the filling into each pepper, pressing it gently to fill the cavity without packing it too tightly. Each half should have a generous, slightly rounded mound of filling. Keep the stuffed peppers upright in the metal pan so the filling stays in place during grilling.

Grill Until Tender.

Place the pan over indirect heat on the preheated grill. Loosely cover the pan with aluminum foil and close the grill lid. Cook at approximately 375°F (190°C) for 15 to 20 minutes, checking around the 15-minute mark. The peppers should begin to soften and become easy to pierce with a fork while retaining their shape. If they're still firm, continue cooking for a few more minutes.

Melt the Cheese.

Carefully remove the foil and sprinkle the 1 cup (113 g) shredded mozzarella evenly over the stuffed peppers. Close the grill lid and cook over indirect heat for another 3 to 5 minutes at approximately 375°F (190°C). The cheese should be completely melted and lightly golden in spots. Remove the pan from the grill once the peppers are tender and the filling is heated through.

Rest and Serve.

Allow the grilled stuffed peppers to rest in the pan for 5 minutes so the filling settles and the cheese firms slightly. Sprinkle the 2 tablespoons (8 g) chopped fresh parsley evenly over the peppers. Use grill-safe tongs to transfer them to serving plates. The peppers should be tender enough to cut with a fork while keeping their filling in place.