For great tapas and delicious prosecco, try Jagajee Tapas and Prosecco Lounge (fun translation of Jagajee: "tickling") on Nimmanheiman Soi 15. Their menu is revolving, but some favorites include marinated mussels in smoked paprika and olive oil, chicken meatballs in curry cream sauce and fried potatoes with red pepper aioli. Tapas are all 50 thb each and well worth it. The staff here are super friendly, especially on slower nights, so sit at the bar and chat awhile.
photo credit: Jagajee