Preheat your oven to 400 F.
Cut a sliver off of the bottom of the bell peppers and the tops off so you can remove the seeds and vein. Dice the tops and set them aside. Put the prepared bell peppers into a baking dish lined with aluminum foil. Roast for about 25 minutes, until the skins start to shrivel slightly. Remove from oven and set aside.
Meanwhile, pour the couscous into a heat-proof bowl and top with 1 cup of boiled water. Cover with saran wrap and allow to sit for about 10 minutes until it has absorbed all of the liquid. Fluff with a fork, then add a pinch each of salt and pepper.
Meanwhile, add the two teaspoons of olive oil to a large nonstick skillet over medium heat. Add in the onions, carrots and celery and saute until softened, about 7 minutes.
Add the ground beef and saute until browned, about 6-7 minutes.
Add the zucchini and the set aside diced bell pepper and cook for an additional 2 minutes, and then add the tomato sauce, and spices. Reduce heat to medium low and cook until the carrots are soft, about another 4-5 minutes.
Add in the baby spinach, lemon zest and juice, raisins, two tablespoons of the nuts, the mint and the cooked couscous. Stir until combined, then season with salt and pepper to taste.
Divide mixture between the bell peppers. Mix together the panko with a teaspoon of oil and the remaining two tablespoons of nuts. Sprinkle on top of the couscous.
Bake for 15 minutes, or until the tops are golden and the filling is heated through. Serve warm.