Preheat oven to 375° F.
Place catfish on a sheet tray, drizzle lightly with olive oil, and season with salt and pepper. Bake for 12 minutes, remove from oven, and allow to cool slightly before flaking into a bowl.
Place dried porcini mushrooms in a small pot, and add stock. Cook over medium-high heat for 15 minutes.
In another larger pot over medium-high heat, melt the butter. Add onions, and sauté for 5 minutes. Add garlic, cremini mushrooms, kosher salt, thyme and tarragon. Cook for 10 minutes, stirring occasionally.
Add porcini and stock mixture into onion and cremini mushroom mixture. Add heavy cream and catfish; stir to combine. Check seasoning, and adjust if necessary. Add lemon juice.
Garnish with thinly sliced green onions.