As all of the veggie restaurants in Zagreb are closed on Sundays we were left with Venera as our only Happycow choice. It was ok. There were 12 veggie pizzas on offer and the two we had were good and pretty cheap. It's a basic cafe style place about 10-15 minutes walk from the cathedral. Recommended, though I'd have preferred to try Vegi Hop down the road if it'd been open..
Cons: A bit out of town