On a cutting board and using a sharp knife, slice the onions, green long peppers and the tomatoes in 4.
Put all the ingredients for the marinade in a mixer, except the butter; the leek sliced in smaller pieces, the garlic, cherry tomatoes, cumin, coriander seeds, pink pepper, rosemary, white wine, Worcestershire sauce, brown sugar, lemon juice and zest, salt and freshly ground pepper and beat until fully pureed.
Put the contents of the mixer in a bowl with the butter and mix together using a whisk until a paste is formed.
Spread the marinade over the leg of lamb and place on two large pieces of parchment paper in a baking dish or pan.
Add the sliced vegetables all around the meat with the chicken broth, salt and freshly ground pepper and wrap tightly with the parchment paper.
Cook in a preheated oven at 150ο C, for 5 hours.
During the last 45 to 60 minutes, open the parchment paper and continue to cook until the meat is golden brown.
Once the meat is ready remove it from the oven, allow it to rest for 15-20 minutes and serve in a large platter with the vegetables in the center of the table.