This mission is available after completing Cesar Vialpando mission for Sweet. You require a Lowrider for this mission, although you might have one already from completing the above mission. If not, you should be able to find one on Cesar's street.
REWARDS - $1000, Lowrider challenge unlocks
Cesar mentions something about a lowrider race (hence why you needed one to start the mission). You'll have to first follow Cesar to the race's starting point. Once you get to the starting grid, the race will start. You'll need to drive through checkpoints as you make your way to the pier in Santa Maria Beach. Each checkpoint has an arrow that will point you in the direction of the next one and the checkpoints show up as red blips on your radar.
You start out in last place and you must finish in 1st place in order to pass the mission. Be careful on the turns and try to avoid obstacles at high speeds with the lowrider, since you tend to lose control when going fast. If you finish in 1st place, you get $1000 for your reward.