While the bread is roasting, prep the sausage and veggies.
In a large skillet, heat 1 tablespoon of olive oil over medium-high. Once the oil is hot but not smoking, add the sausage. Cook, undisturbed, for 4 minutes or until a deep golden crust forms on one side.
Flip, breaking the sausage up with a spatula, and continue to cook for another 3 to 4 minutes, or until the sausage is cooked through. Using a slotted spoon, transfer to a large plate.
To the same skillet, add another 2 tablespoons of oil and 2 tablespoons of ghee.
Add the mushrooms and spread into an even layer. Cook, undisturbed for 4 minutes until one side of the mushrooms is a deep, golden brown.
Stir the mushrooms and season with 1 teaspoon of kosher salt. Continue to cook, stirring occasionally, until most of the liquid has evaporated and the mushrooms are a rich brown, about 4 more minutes.
Transfer to the same plate as the sausage and set aside.
Turn the heat beneath the skillet down to medium and add the remaining tablespoon of olive oil and 4 tablespoons of ghee.
Once the ghee has melted, add the onions and celery. Season with the remaining teaspoon of kosher salt, black pepper, and Italian seasoning. Cook, stirring occasionally, until the onions are translucent and soft, about 7 minutes.
Add in the garlic, sage, and thyme. Stir to combine and cook for 1 minute, or until the herbs and garlic are fragrant. Remove from the heat and stir in the lemon juice.