If the raw bajra and moong dal are cooked together, the bajra won’t get cooked all the way and the moong dal will be overcooked and become lumpy because moong dal cooks faster than bajra. Also, since the moong dal becomes overcooked and thick, it gets stuck at the bottom of the cooker, causing it to get browned or burnt. If you don't want to cook them separately, you can soak bajra overnight and then cook them together. For soaking, I suggest to grinding the pearl millet first and then soaking the coarsely ground bajra. If you soak first and then grind, then you may get a mixture like bajra batter.