How do you make restaurant style red sauce with onions.?!

Can anyone tell me how you make the red sauce that is traditionally served at Indian/Pakistani restaurants with onions. Some people have said it's made from ketchup... I'd also like to know how they make the red chilli sauce. It doesn't taste anything like the chilli sauce you buy from the shops.
Restaurants like Akbars and Al Faisals serve these types of chutneys and they're delicious