Bring to a simmer, and cook over low heat for 5 minutes. Allow mixture to cool slightly. In food processor bowl, pulse mixture three times, just enough to break up the tomatillos. Be careful not to puree the mixture. Season halibut with salt and pepper.
Place steaks in a steamer over simmering water and cover.
Steam for 8 to 10 minutes, until fish is cooked through. Place steaks on plate and cascade sauce over top of steamed fish. Makes four servings. To make salsa, combine all ingredients in small bowl. Cover and refrigerate while making the sauce and cooking the halibut.