Take him for walks in secluded areas by yourself if you can. Build upon your trust and recall with him.

I'd do this for months do you both get to know each other.

Yes it's very boring but you want long term success. At some point you're going to natural bump into other dogs anyway. But at least it won't be in a dog park where things could get messy.

Good luck

Have you tried doing some training with him 10-15 minutes before taking him out for his walk?

The training (sit / stay etc) will tire the brain and he'll want to sleep. But before he does take him for a walk.

He may just be too tired to do what he currently does...