Pat fish dry with a paper towel. Season with salt and ground pepper.
Add oil to a large cast iron and heat on medium high until shimmering. Place steelhead skin side down and cook for 3-4 minutes. Flip and cook for another 3 minutes or until golden brown.
Remove fish from the pan and set aside. Using the same pan, bring heat to low, add butter and chopped onions until translucent.
Add chopped sundried-tomatoes, tomato paste, artichokes and spinach. Mix for 1 minute and add vegetable broth. Reduce the heat to simmer and stir until the spinach is wilted. Now stir in the cream and cook for 1 minute more.
Carefully return the cooked steelhead to the pan, nestling it into the sauce and place the entire pan in the oven at 350° until heated (~3 minutes).
Add salt, pepper and lemon to your taste. Top with chopped parsley.
Pour the sauce on top of the fish and serve warm.