Green’s Dictionary of Slang

a cucumber.

1960, 1975		Wentworth & Flexner DAS 134/2: cuke n. A cucumber.
1981		A.K. Shulman On the Stroll 280: Look for cukes going soft, burst-open peppers.
1993		S. King Dolores Claiborne 231: Amongst the beans n cukes.