Use the “sauté function on your instant pot or pressure cooker to cook the onions in 2 tablespoons of olive oil, until browned and softened (about 3 minutes).
Add the pepper, spinach, and garlic. Sauté until fragrant (about 30 seconds).
Add the chicken stock, tomatoes, tomato paste, olives, white wine, basil, and fennel seeds.
Turn the “sauté” function off, cover and seal your Instant pot, and set manual pressure to “high” for 5 minutes.
Once your pressure cooker is done, quick release the pressure until the float valve is depressed.
Open the instant pot and turn the “sauté” function back on. Once the broth mix is simmering (which shouldn’t take long since it’s piping hot already), add the fish pieces and simmer for about 5 minutes, until fish is just cooked and flakes apart easily.
Turn off “sauté” function and stir. Taste and adjust seasoning if necessary.
Serve immediately