Osso, the co-offensive coordinator at Corona del Mar last season and an assistant at Beckman for the 2004 season, said he had his eye on rejoining the Mustangs for a long time.
"I was actually about to become Jay's offensive coordinator when he left," Osso said. "I'm not going to lie, this is something I coveted. I was here under [former coach Dave] Perkins and I loved the people I worked with. Ever since I left, I was looking for a way to come back."
Osso was an assistant at Estancia under Perkins and came to Costa Mesa when Perkins was hired there in 2001.
Osso inherits a team that went 2-8 last season, including an 0-7 start.
The Mustangs haven't been to the playoffs since the 2002 season, and haven't won a playoff game since 1997.
Costa Mesa will join the newly-formed Orange Coast League in the fall, along with Estancia, Laguna Beach, Calvary Chapel and Godinez.
"I just finished telling [the players] they're the ones who determine wins and losses," Osso said. "They can play football. What we're trying to accomplish is teaching them the right technique. We're trying to improve on last year, and make them more competitive. We're trying to put them in position to win games."
Osso becomes the Mustangs' fifth head coach this decade, following the departures of Jerry Howell, Perkins, Tom Baldwin and Johnson.