Add farro to a small saucepan & cover with 1 inch cold water. Bring to a boil, reduce heat to low, & cook until the grains are tender, 15-18 minutes. Drain any excess water.
Thinly slice sausages into rounds. Heat 1 Tbsp olive oil in a large nonstick skillet over medium-high heat. Add sausage and cook, 5-6 minutes. Transfer sausage to a plate.
Slice mushrooms. Peel and mince shallot. Dice apple. Return skillet to medium-high heat with 2 Tbsp olive oil. Add mushrooms & cook until softened, 3-4 minutes. Add shallot, garlic, apple & a pinch of salt & pepper. Cook, tossing occassionally, until the apple is carmelized in places, 4-6 minutes.
Add vinegar to skillet & cook until it evaporates, about 30 seconds. Add cooked farro, spinach, and mustard & herb blend and toss well. Cook until spinach is wilted, 3-4 minutes.
Top farro, mushroom, apple, & spinach mixture with sausage.
