Season the sirloin with salt and pepper. Heat 2 tablespoons oil in a skillet over medium heat, add the steaks and sear on both sides until golden.
In the meantime, heat the oil in a skillet over medium heat; add onion, garlic, paprika and oregano, and sauté for 5 minutes or until the onion looks translucent. Add ají amarillo paste, stir, and after 3 minutes add tomato, cooking for 5 more minutes. Add wine, bring to a boil, lower the heat and simmer for 3 minutes. Season with salt and pepper.
Add fish stock and simmer for 10 minutes. Dissolve potato starch in 3 tablespoons cold water, add to the saucepan and stir until it is slightly thick. Finally add the mussels, scallops, shrimp, and squid, stir and steam for a few minutes, just until the mussels open their shells, the scallops look opaque, and the shrimp turn pink, about four minutes.
Sprinkle with cilantro, salt, and pepper. Turn off the heat.
Transfer the sirloin medallions to 4 plates, surround with the seafood sauce, and serve immediately.
** To make fish stock put the bones and heads of the fish in a saucepan, cover with water, add two parsley sprigs, 1 celery rib, and ¼ onion. Bring to a boil over high heat, turn the heat to low and simmer for 25 minutes. Strain and discard the solids.
Recipe by PERU DELIGHTS at https://perudelights.com/sirloin-medallions-with-macho-sauce-a-seafood-feast-for-brave-men/