Adjust rack to middle position and preheat oven to 425 degrees. Wash and dry all produce. Halve bell peppers lengthwise; remove core and seeds. Place on a baking sheet and drizzle with oil. Season with salt and pepper. Roast until browned and softened, about 20 minutes.

Melt 1 TBSP butter (2 TBSP for 4 servings) in a small, lidded pot over medium-high heat. Add couscous and a pinch of salt and pepper. Cook, stirring, until toasted, 2-3 minutes. Add 3/4 cup water (11/2 cups for 4) and bring mixture to a boil. Once boiling, cover, reduce heat to low, and cook until tender, 10-12 minutes. Keep covered until ready to serve. Meanwhile, halve, peel, and dice onion. Finely dice tomato.

Heat a drizzle of oil in a large pan over medium heat. Add onion and cook, stirring, until softened, 4-5 minutes. Add beef and Tuscan Heat Spice; season with salt and pepper. Cook, breaking up meat into pieces, until browned and cooked through, 4-5 minutes. Carefully pour out and discard any excess grease, leaving filling in pan.

Stir tomato paste and diced tomato into pan until thoroughly combined, then add stock concentrate and 1/3 cup water; season with salt and pepper. Simmer until slightly thickened, 1-2 minutes. Stir in couscous until thoroughly combined. Turn off heat.

Once bell peppers are done roasting, stuff each half with as much filling as will fit. Place in pan with remaining filling, nestling each stuffed pepper half in the mixture. Sprinkle evenly with mozzarella. TIP: If your pan isn’t ovenproof, transfer mixture to a small baking dish and arrange stuffed pepper halves in there.

Bake stuffed peppers on middle rack until cheese has melted, 3-4 minutes. Divide pepper halves and remaining filling between plates and serve.