Heat oil in a medium saucepan. Add onions and cook, stirring occasionally until they begin to wilt. Add garlic and ginger and saute 30 seconds. Deglaze with vinegar and evaporate.
Stir in coriander, cumin, lentils and broth. Bring to a boil, reduce heat to low and simmer, covered, until lentils are tender and soupy, about 10 to 15 minutes; season to taste with salt and pepper.
Meanwhile, cook pasta. When done, drain pasta and return to pot, off heat; toss with butter and lentils; adjust seasoning. Serve out a portion and garnish with mint.