Set out the fish on the kitchen counter to defrost and proceed with the steps listed below. By the time you gather all the ingredients and get to to the fish, it should be somewhat defrosted and ready for you.
Rinse the rice well and drain. Place the rice, water, salt, and oil in the inner liner of the instant pot and stir to mix.
Cut 4 pieces of aluminum foil large enough to hold and wrap the fish in a pocket. Divide the spinach evenly between the four sheets. Place the fish on top. Drizzle oil, salt and pepper on top of the fish and close each packet. Close up the packets of foil into long rectangles, ensuring the packages will not leak (otherwise your rice is going to taste entirely too fishy).
Place a steamer rack on top of the rice. Place the aluminum packets of spinach and fish on the steamer rack in one layer.
Cook for 4 Minutes high pressure.
Allow it to release pressure naturally for 10 mins and then release all remaining pressure.
For the Sauce: While the rice and fish cook, mix together the mayonnaise, garlic and lemon juice and let it rest.
To serve, divide the rice into four bowls. Spoon the spinach and fish from each packet onto the rice, pouring any juice in the package on the rice, and drizzle with the sauce, if using. Or you know, let everyone get their own fish—you’ve already done the cooking for them!