Heat oil over medium heat in a large skillet. Cook and stir yams in the hot oil until 1 side is golden, about 5 minutes. Add onions and saute until softened and golden, about 5 minutes, or longer if you like more color. Stir in eggplant, coriander, cumin, red pepper flakes, and salt. Cook and stir mixture until glaze is just about to burn, 5 to 7 minutes more.

Reduce heat to low and deglaze the pan by pouring in some of the hot water and scraping up browned bits. Add red lentils and remaining water. Cover and let simmer until lentils and vegetables are soft, about 30 minutes.