Heat a pot of water to a boil. Season it with salt and pepper. Meanwhile heat a skillet over medium heat with some olive oil. Medium dice the shallot, pick the sage leaves off of the stems, zest and halve the lemon.
Cut the sausage out of its casings and add to the skillet. Brown the meat through, breaking it down thoroughly. Once browned and lightly crisped, remove the meat from the pan to a paper towel lined plate.
Place the pan back on the stove, turn the heat to low/medium and add the butter. Once the butter is melted, add the mushrooms, shallot, garlic, and the juice of the lemon. Season with salt and pepper. Cook, stirring frequently, until the mushrooms and shallots are browned.
While cooking the vegetables, heat a small pan with a thin layer of olive oil over medium heat. Add the sage leaves frying until they're fragrant and lightly browned. Remove from the pan and add to a paper towel lined plate.
Add the gnocchi to the boiling water and cook according to the package. Add the meat back into the skillet to reheat, along with the sage oil and lemon zest. Once cooked add the gnocchi to the skillet. Stir in the parmesan cheese. Plate the pasta and top with some more parmesan and the crispy sage.