How did the disciples recognize the resurrected Jesus while fishing?

The resurrected Jesus appeared ordinary, so the disciples did not recognize Him by sight. After He told them to cast the net on the other side, the catch came full, and Peter declared, 'It's the Lord!' Recognition came through that miraculous sign, not His outward appearance.

Les explains that Jesus looked very common and ordinary in His post-resurrection appearances, not bizarre or weird. The disciples saw Him cooking fish on the shore and did not know who He was; they even asked if He had any food. Only after He told them to put the net on the other side and the net came full did Peter say, 'It's the Lord!' Les notes Jesus then ate breakfast with them, showing He had the outward appearances of another human being though He was now immortal. Their recognition was therefore tied to the miraculous catch, not His appearance.

Why didn't the disciples recognize Jesus when He was cooking fish on the shore?

They did not recognize Him because His resurrected body looked completely normal and ordinary, not bizarre or strangely different. He appeared like just another human being, with all the outward appearances of a man, so they could not identify Him until the miraculous catch of fish prompted Peter to say, "It's the Lord!"