Caçarola is the closest thing I found that looks like a bistro in Luanda. It is a small restaurant/bar in a U-shape with about 15 seats, and the welcoming barman/owner behind the counter brings you drinks and food with a smile and a chit-chat. It is on my way to the office so for me it’s a nice place to have a beer after work. The food is ok for snacks, less for main dishes, and everything is very cheap (a coke for 100 kwanzas, a sandwich for 300 kwanzas, etc..)
Recommended if you live nearby. I didn’t feel so safe right outside the bar though and I got a little harassed by a lonely guy once. Be careful without being paranoid.