Thai sweet chili sauce is a thick, bottled sauce that has a sweet flavor with a spicy kick from chili flakes. You can usually find it in the Asian food section of your grocery store or you can buy it online. If you can't find it, you can try substituting hot sauce (like Sriracha) mixed with honey. You can also try plum sauce or hoisin sauce mixed with a little hot sauce or chili flakes. Apricot preserves mixed with hot sauce (like Sriracha) will also give a similar sweet and spicy flavor profile.