In a small bowl, whisk the wine with the lemon juice, berbere, paprika and mustard.
Season the lamb with salt and pepper. In a large enameled cast-iron casserole, heat the olive oil until shimmering. Add half of the lamb to the casserole and cook over moderately high heat, turning, until browned all over, 6 to 8 minutes. Using a slotted spoon, transfer the lamb to a medium bowl. Repeat with the remaining lamb.
Add the onions, garlic, rosemary, thyme and a generous pinch each of salt and pepper to the casserole and cook over moderate heat, stirring occasionally, until the onions have softened, about 8 minutes.
Add the lamb and any accumulated juices to the casserole along with the wine mixture, tomatoes, bell pepper and shallot. Cook over moderate heat, stirring, until the tomatoes and bell pepper have softened and the lamb is just cooked through, about 10 minutes. Season with salt and pepper and serve.