Gary Hall also claimed his second Continental Open medal of the year during an impressive weekend in Morocco.
Victory in the -100kg weight division was the perfect way for Fletcher to celebrate his 24th birthday.
“It was a good day’s judo – I’m not sure it’s the best I’ve ever fought but I got the job done,” he said.
“It was really good in terms of getting points for Rio and to win it on my birthday just added to it!”
Fletcher has now won three gold medals in Africa during the past 14 months. He overcame Slovakia’s Miroslav Dzur, Luca Ardizio of Italy and Croatia’s Zlatko Kumric en route to the final, where he beat Italian Domenico Di Guida.
Nartey, who is also coached by Juergen Klinger at the University of Bath Sports Training Village, won gold for Ghana in the -73kg category.
He beat Spanish fighters in both the semi-final and final, Dasnel Gonzalez Martinez and Javier Ramirez respectively, having earlier overcome Alaa Bassou of Morocco, Montenegro’s Nikola Gusic and Portugal’s Jorge Fernandes.
Victory strengthened Nartey’s grip on the African continental quota qualifying place for this summer’s Olympic Games – he also represented Ghana at London 2012.
“It was a good tournament and a big step forwards for both Ben and Mani,” said coach Klinger. “Both overcame difficult opponents – Ben beat the European U23 Champion in his final – and Mani’s performance was very concentrated.”
Hall, meanwhile, repeated his -90kg bronze-medal placing from January’s African Open in Tunis to continue his good start to the year.
After a first-round win over Cameroon’s Dieudonne Dolassem, defeat to Abderrahmane Benamadi of Algeria in the quarter-finals sent Hall into the repechage.
He responded well, though, beating Spain’s Pedro Gonzalez Navarro before winning his bronze-medal contest against Milan Randl of Slovakia.
Tom Reed finished seventh overall in a packed -81kg weight division. He beat Burma’s Hermann Monne and Diego Frustaci of Italy to reach the quarter-finals.
“This was Tom’s first tournament after an elbow injury and he fought really well,” Klinger added. “It will have given him a positive feeling to be back on the mat.”
Klinger’s squad will next be in action at the Grand Prix in Tbilisi, Georgia over the Easter weekend.