To serve 4 you will need:
2 large firm beef tomatoes
2 large yellow bell peppers
2 large red bell peppers
100g shelled pistachios
4 cloves garlic - chopped
200g long grain rice
1 teaspoon dried oregano
1 fresh red chilli - deseeded and finely chopped
sea salt and freshly ground black pepper
600ml chicken or vegetable stock - I used Knorr stock cubes
200g Greek feta cheese, crumbled
small bunch of mint - leaves picked and finely chopped
small bunch of flat leaf parsley - leaves picked and finely chopped
1 tablespoon of tomato puree (tomato paste if you are in the US)

Preheat your oven to 200C/400F/Gas 6
 
How to do it:

Cut the tops off the tomatoes and put then to one side.  Use a spoon to carefully hollow out the inside and get rid of that bit.
Halve the peppers lenghtways, keeping the stalks intact. With a sharp knife and a spoon, carefully get rid of the seeds. 
Place all these vegetables into an appropriately sized deep sided oven dish.  You want them to fit nice and snug.
 

Toast the pistachios in a dry frying pan, keeping them moving so they don't burn.  When they're done tip them into a pestle and mortar and roughly crush, then put them to one side.
 
Add a glug of oil to the pan, put it back on a low heat and add the onions and garlic.  Cook for about 10 minutes, until the onion is soft but not coloured.
Add the rice, oregano, chilli and a good pinch of salt and pepper.  Pour in half of the stock (300ml) and cook for around 7 to 10 minutes, stirring constantly, so the rice gets coated
in everything and doesn't stick to the pan.
Remove from the heat and stir in the crumbled feta, fresh herbs and bashed up pistachios.

Carefully stuff the hollowed-out peppers and tomatoes with the hot rice mixture so it comes just to the top. 
Don't over fill them as the rice will expand when it cooks.  Put the tops back on the tomatoes and drizzle a few glugs of oil over the lot.

Mix the tomato puree/paste with the remaining stock and pour into the baking dish, around, not over the veg.
Cover tightly with kitchen foil and bake in the hot oven for around 1 hour and 15 minutes.  Remove from the oven and transfer to serving plates. 

Serve straight away with nice salad and fresh crusty bread.