The Columbians are selling Spank through coffee stands, and Asuka wants you to bust them up.
Once you hit the first stand, you will have eight minutes to finish busting up the rest. There are nine stands total; two in Portland (next to the Portland Docks and next to the entrance to Salvatore's mansion), five in Staunton (next to the parking garage, inside the park, in front of the church, on the street by the church and near the star-shaped statue by Kenji's casino) and finally two in Shoreside (near the subway entrance and at the hospital).
Since there is no time limit before you start busting up the shops, you can drive around and get them on your radar before you start if you wish. I suggest starting with the hospital one in Shoreside, moving on to Staunton and then Portland, using the bridges to get to the islands instead of the tunnel. The easiest method for most of the stalls is to run into them with your car, but for a couple of them (like the one in Belleville Park), it's easier just to lob a grenade at the stall. Just be careful, since the Columbian in each stall will open fire as soon as he sees you.
This mission is pretty easy once you know where the stalls are; the only part you really have to be careful on is the stall in front of Salvatore's mansion, since the Mafia and their shotguns can quickly blow up your car. My best advice is to get a new car before you go for it (this should probably be the last stall you destroy), hopefully one with decent armor, and haul ass. If you are close to the stall and your car is on fire, I would say to try and hit the stall, since you still clear the mission as long as the stall is destroyed