Start by preheating your oven to 425°F and positioning the rack in the middle.
Mix the ground beef with 1 teaspoon salt and baking soda, then let it sit for 20 minutes.
Prepare a baking dish with foil (optional for easy clean-up), place the peppers cut side up, drizzle with 1 tablespoon oil, and sprinkle with the remaining salt.
Roast the peppers for 20 minutes until they're tender but still hold their shape.
While peppers roast, cook the onion in the remaining oil until soft, then add garlic, spices, and beef. Cook until browned, then add tomato sauce and cook until the beef is done.
Mix in the cooked grain and half the cheese into the beef mixture until the cheese is melted.
Fill the roasted peppers with the beef mixture, top with the remaining cheese, and bake until the cheese is bubbly.