TheFork users who ate in Orvault have said really good things about Le Mas des Oliviers, Le Cambronne Bistrot Chic and Coin de Jasmine. Maybe you should give them a try!
Some of the more popular Falafel restaurants having a terrace in Orvault according to TheFork users include:
Le Mas des Oliviers, with a 9.2 rating
Le Cambronne Bistrot Chic, with a 9.3 rating
Coin de Jasmine, with a 9.2 rating