In a medium pot, heat oil over medium heat. Add garlic and onions and saute until onions are transparent, 2 to 3 minutes.
Add chile powder, paprika, chile flakes, cayenne, cumin and coriander; saute, stirring constantly, about 2 minutes more.
Add lamb and stir and mash constantly with a wooden spoon to break it up into very fine particles, until evenly browned, 5 to 7 minutes.
Stir in lentils, broth, tomatoes, oregano, rosemary, salt, sugar, and pepper; bring to a boil, then reduce heat to low and simmer, stirring occasionally, until lentils are tender and chili is thick, about 30 minutes, adding some water to pot if lentils absorb all liquid before chili is done.