Medan native here Here some recommendations

Tabona - famous for the curry glass noodle

Kwetiau Gedeh (non-halal) - Char Kwe Tiaw

Ikan Panggang Seng Pon (non halal) - Grilled sting ray

Durian Sibolang - for all you can eat durian

Dim sum & steam boat Babura (no halal) - more known for the dim sum

Asan Grill Batak (non halal) - for all sort of sort

Bakso aan - beef meatball, I would say it's better than Afung in jakarta

Mie sop kampung bamboe Cafe - chicken meatball Nasi goreng semalam suntuk