Add to blender onion, ginger, garlic form into smooth paste. Saute paste in olive oil over medium heat 5 minutes. Add turmeric, coriander, cumin and chili powder, continue to saute for 5 minutes. Add tomatoes, chicken and fry until chicken has browned on all sides. Add water, cinnamon, cardamom, salt and bring to boil. Cover and simmer 25 minutes. Saute the sliced onion until brown, stir it into sauce along with cilantro and serve.