Melt ghee in the skillet over high heat. Add mushrooms and salt; cook, without stirring, until they release their moisture, 1 to 2 minutes. Continue cooking, stirring occasionally, until browned, 5 to 8 minutes. Add shallots; cook and stir until fragrant, about 2 minutes.
Mix avocado into the mushroom mixture; cook and stir until avocado is creamy, about 5 minutes. Season with salt and ground black pepper.
Bacon fat or lardons can be substituted for the ghee.
If using lardons, cook in a skillet over medium-low heat until crisp, about 5 minutes. Transfer to a paper towel-lined plate. Reserve 2 tablespoons of grease in the skillet for cooking. Add lardons back into the skillet with the avocado.