Heat the oven to 150°C fan
In a pestle and mortar, grind garlic, chilli, thyme, lemon zest, half the lemon juice, salt, anchovy and its oil into a paste
Rub the paste over the underside of the lamb and roll up, then tie securely with string
Brown off the rolled lamb in a little olive oil in the pot you're going to roast it in
Remove the lamb and fry off the onion, celery, lemon zest, and saffron in the same pan
Add the wine to deglaze, followed by the stock and tomatoes
Return the lamb to the pot, cover with a lid and roast for 3 hours
Remove from the oven, add orzo, stir to coat in the liquid, then return to the oven for 10 minutes
Chop the fresh herbs and stir them into the juices with the peas and remaining lemon juice
Cover again and roast for a few more minutes until the peas are cooked
