There are very few places in Mumbai where they actually get Punjabi food right, Nothern Tadka is one of them. Like someone below mentioned, it's owned by the same people who own Urban Tadka, so if you've liked the food there, you'll like the food at Nothern Tadka.
The decor resembles a Punjabi village and if you visit for the first time, I'm pretty sure you'll find the menu a little funny. Unfortunately I can't remember what kind of music they were playing there when I visited last week.
My personal favourites are the Dal Makhani and the Alu Chhole Biryani. I tried their special nimbu paani (lemonade), which was tasty, but it had a little chilli powder or something that didn't really make it spicy, but it hit my throat and made me cough a little.
They have happy hours till 11pm.
A tip - on weekends, it can get packed, so I'd recommend going their a little early.