Pour water into your Instant Pot® and place a steamer basket inside. Drizzle the cod fillets with olive oil, then season with chili powder, salt, cumin, garlic powder, pepper, and lime zest. Place the fillets in the steamer basket.
Secure the lid on the Instant Pot® and ensure it’s locked in place. Press the Pressure Cook button and set the timer for 5 minutes. When the timer beeps, perform a quick release of the pressure until the float valve drops. Then, unlock and remove the lid.
In a medium bowl, whisk together the lime juice, mayonnaise, and sour cream. Gently fold in the cabbage to create the slaw.
To assemble the tacos, place an equal amount of cod on each tortilla and top with the cabbage slaw. Garnish with cilantro and serve warm.