Remove the meat from the fridge approx. 1 hr. before cooking. Put the peas and all the other ingredients up to and including the parsley into a mixer bowl, puree, season.
Mix the mustard, oil and rosemary. Rub the mixture into the meat, season. Spread the filling over the lower middle part of the meat, roll up tightly, tie with kitchen string, place in a casserole dish.
Roast for approx. 20 mins. in the centre of an oven preheated to 220°C. Reduce heat to 160 °C and cook for a further 50 mins.
Heat 1 tbsp of butter in a pan. Sauté the peas, season with salt, pour in the water, simmer for approx. 10 mins. until soft. Puree ⅔ of the peas, stir the rest of the peas in with the remaining butter and lemon juice.
Simmer the rice in salted water for approx. 20 mins., drain. Mix the butter and parsley into the rice.