Season the lamb with salt and pepper and set aside. In a large stockpot, heat the olive oil over medium high heat. Add in the lamb and brown on all sides.
Add the garlic and diced onions and cook the onions until soft, about 8 minutes.
Add the flour, mixing it through and cooking about 1 minute to get the raw flavor out.
Add in the wine and cook for 2-3 minutes, scraping the bottom of the pot with a wooden spoon.
Add in the stock, tomatoes, rosemary, thyme and bay leaf. Bring to a boil, then reduce to a simmer; cover and cook until the meat is tender, about 1 ½ hours.
While the meat is cooking you can prepare the vegetables to have them ready. Bring a small saucepan of water to a boil, and add pearl onions. Boil 2 minutes, and drain. When cool enough to handle, peel and set aside.
Peel the carrots; trim tops and cut diagonally into 2 inch pieces. Repeat with turnip.
Remove the meat and place in a large bowl and set aside. Taste the sauce and make any seasoning adjustments. Skim off any fat.
Strain the sauce over the meat, pressing with your spatula to get all of the sauce out and then discarding any solids and return the meat and sauce back into the pot. Make sure to run your spatula on the bottom of the strainer to get all of the delicious sauce stuck on the bottom.
Add onions, turnips and carrots to casserole and simmer, covered, for 15 minutes.
Add in peas, and simmer 5 minutes more, or until vegetables are tender.
Blanch beans until bright green and still crisp, then drain. Serve stew over mashed potatoes, and scatter beans atop each serving. Garnish with the chervil or parsley, and serve.