Bring 2 cups water to a boil. Add dried mushrooms. Turn off heat, let sit 20 minutes while preparing the rest of the ingredients.
Strain the liquid and reserve. Coarsely chop the mushrooms.
Collards
In a large, heavy-bottomed sauté pan, heat 2 tablespoons avocado oil over medium-high heat until shimmering.
Add sliced mushrooms and reserved rehydrated mushrooms (from stock) and cook, stirring, until lightly browned, about 8 minutes.
Add onion and garlic. Sprinkle with salt and cook, scraping up any browned bits, until softened, about 3 minutes; lower heat if necessary to prevent burning.