Trim fat from lamb, and cut into 1-inch cubes. Set lamb aside.
Heat oil in a Dutch oven over medium heat until hot. Add onion, celery, and garlic; sauté 2 minutes. Add lamb; sauté 5 minutes or until browned. Add curry, cumin, and pepper; stir well to coat. Add broth, lentils, and tomatoes; bring to a boil. Reduce heat; simmer, uncovered, 20 minutes, stirring occasionally. Add greens and carrot; simmer 10 minutes or until lamb is tender. Remove from heat; stir in chopped cilantro. Garnish with cilantro sprigs, if desired.
Note: The purchase weight of lamb is 1 1/3 to 1 1/2 pounds to equal 1 pound, trimmed.