Press Sauté; the indicator will read “Normal.” When the display says “Hot,” add oil to the pot and heat until shimmering. Add pork and cook, breaking it up with a spoon, for 3 minutes. Add shrimp and cook, stirring, for 2 to 3 minutes or until pork is no longer pink and shrimp are transparent. Add garlic and ginger; cook, stirring, for 1 minute or until fragrant. Press Cancel.
Transfer filling to a bowl and add teriyaki sauce and fish sauce (if using), mixing well. Wash and dry the inner pot.
Working in batches, place wonton wrappers on a plate and add about 1 tablespoon (15 mL) filling to the center of each. Using your fingers, brush the edges of the wrappers with water and fold into a triangle, squeezing out air and pressing down edges to seal. Repeat until all wrappers are filled.
Add 1 cup (250 mL) water to the inner pot and place the steam rack in the pot. Place about 12 filled wontons on the rack, overlapping slightly. Close and lock the lid and turn the steam release handle to Sealing. Press Steam; the indicator will read “High Pressure.” Use the – button to decrease the time on the display to 5 minutes.
When the timer beeps, press Cancel and turn the steam release handle to Venting. When the float valve drops down, remove the lid. The wontons should be hot and steaming. (If more cooking is needed, reset the steamer to “High Pressure” for 1 minute.) Transfer wontons to a serving platter, cover with foil and keep warm. Add water as necessary to maintain 1 cup (250 mL) water in the bottom of the pot. Repeat with the remaining wontons. Serve sprinkled with green onions.