Slice the spam in half and then into thick pieces.
In a bowl, mix the low sodium soy sauce, rice vinegar, and sugar until the sugar is dissolved.
Heat a skillet over medium heat. Place the spam slices and cook for about 2-3 minutes on each side until they are golden brown.
Pour the soy sauce mixture over and let it cook for an additional 1-2 minutes, allowing the spam to absorb the flavors. Remove from heat and let it cool slightly.
Wet your hands and the inside of the onigiri mold with water to prevent the rice from sticking.
Place a scoop of rice into the mold, filling it about halfway.
Add a slice of spam on top of the rice layer in the mold.
Add more rice on top, filling the mold to the top.
Press down firmly to form the onigiri shape.
Take an onigiri wrapper and follow the instructions on the package for wrapping.