For herb crust, combine breadcrumbs, lemon zest, rosemary, thyme, garlic and melted butter in a medium bowl. Season with salt and pepper. Place lamb onto a chopping board and trim off excess fat. Turn over and season well with salt and pepper. Brush underside with mustard and top with 2/3 of the herb crust mixture, pressing down with fingertips.
Place tomatoes in a small oven-proof serving dish and fill each with remaining herb crust mixture.
When vegetables have roasted for 20 minutes, remove from oven and place lamb on an oven rack placed over vegetables and return to shelf in oven. Place tomato dish on lower shelf. Roast together for 30 minutes or until cooked to your liking.
For peas, melt butter in a small saucepan and add lettuce. Cook until soft. Add peas and ½ cup of water, cover and simmer over a low heat for 8 minutes. Strain into a small bowl.
For sauce, remove vegetables from roasting pan leaving the liquid and garlic. Add stock and verjuice and deglaze the pan, stirring. Squash garlic cloves with the back of a spoon and. Strain mixture into a saucepan and bring to a simmer over a high heat until reduced. Pour into a jug.
To serve, arrange meat on a clean chopping board, place peas in a small dish next to meat and pour sauce into a small jug and place next to meat. Serve vegetables and tomatoes in separate serving dishes and arrange dishes next to chopping board.