Wash the peppers, but leave them whole. Place them on a baking tray, and drizzle lightly with a dash of oil. Roast at 190°C (Gas Mark 5 / 375°F) for about 10 minutes, until slightly soft. Set aside until cool enough to handle.
Meanwhile, prepare the herby risotto. Heat the oil in a large frying pan or wok, and add the onion and garlic. Cook over a medium heat for a few minutes until softened, then add the rice, and cook for a further 2 minutes.
Add the vegetable stock to the rice a little at a time, stirring regularly and only adding more stock when any excess liquid in the pan has been absorbed. It should take around 25 minutes in total for the rice to absorb all of the stock and to be fully cooked - add a dash more water if the rice isn't completely cooked by the time you've used up all of the stock.
Add the spinach and basil to a food processor, and blitz until finely chopped. Add this mixture to the risotto, along with the grated cheese. Mix well and cook until the cheese has melted.
When the peppers are cool, slice them down one side, and carefully remove the seeds (don't worry if one or two seeds remain). Fill each pepper with risotto, and sprinkle with pumpkin seeds or pine nuts. Return to the oven for a further 10 minutes, or until the peppers and risotto are cooked to your liking.