1)Instead of Pressure-cooking dal, you shall cook in closed pan. But this requires more water and more cooking time, around 20+ minutes.
2)Start peeling raw banana just when the onions are frying, so that once cut, you shall directly add it to the pan. If you peel and chop in advance, it will turn darker. You shall put the chopped pieces inside water, until required to avoid color change.
3)Increase or decrease chillies as per your spice level.