Heat oil and add the mustard seeds
When they pop, add the urad dal, if using
When the urad dal turns golden brown, add the onions and curry leaves
Saute until the onions turn soft and transparent. No need to brown them or fry them too much
Now add the chopped capsicum and cook for 3-4 mins until it turns a bit soft and gets semi-cooked
Top up with the masala powders - chilli, coriander, cumin, turmeric, amchoor (if using), hing - and some salt
Mix well and fry on low heat for a minute or two
Now add the besan and mix again
You will find the mixture to be a bit dry so keeping flame low, add water one tablespoon at a time until the mixture turns moist. Don't add too much water, it will make the sabji too watery
Keep stirring frequently and you will find the besan coming together with the other vegetables and cooking through
Taste to make sure no more salt is required
Remove from heat and serve warm