Cut the tops off the peppers (keeping the tops to one side) and remove the seeds and any white flesh from inside. Use a small sharp knife to carve spooky Halloween faces into the sides. Chop any offcuts into small pieces and set aside.
Toast the pine nuts in a dry pan for a few mins until golden, and set aside. Heat the oil in the pan, and heat the oven to 200C/180C fan/gas 6. Cook the onion in the oil for 8-10 mins until softened. Stir in the garlic, pepper offcuts and aubergine and cook for another 10 mins, until the veggies are soft. Add a splash of water if the pan looks dry. Season.
Squeeze the pouch of grains to break them up, then tip into the pan with the tomato paste. Stir for a minute or two to warm through, then remove from the heat and add the lemon zest, basil and pine nuts.
Fill each pepper with the grain mixture. Replace the lids, using cocktail sticks to secure them in place, and put the peppers in a deep roasting tin with the carved faces facing upwards. Cover with foil and bake for 35 mins, uncovered for the final 10. The peppers should be soft and the filling piping hot.