Gather all the ingredients.
Pat down any juice on cod with a paper towel and sprinkle salt and pepper evenly on both sides of the fillets. Set aside.
Cut onions into smaller blocks and add to food processor.
Use a peeler to de-skin ginger. Cut into smaller blocks and add to food processor.
Zest lemon with a zester and add to food processor. Use the same lemon to add 1/4 tsp lemon juice into the food processor.
Add Swerve/Monkfruit, Soy Sauce and Rice Vinegar into a food processor. Pulse until desired consistency is reached (we blend for about 20-30 second) and transfer to a serving bowl.
Add Sesame Oil to cast iron pan and heat on high (please note that cast iron pan & handle gets VERY hot. So please wear mitts if you need to handle the pan).
When cast iron is ready, the oil should be lightly smoking. Reduce heat to medium-high and carefully place cods into cast iron pan (please note oil will splatter so take precaution). Cover and cook for 2-3 minutes (depends on thickness). When searing, do not move the meat.
After 2-3 minutes, carefully flip the cod, re-cover and cook for an additional 2-3 minutes.
Carefully transfer cod to a serving plate and serve with ginger sauce.