Place some oil into the frying pan. Place on medium-high heat. Once its hot, add in garlic slices. After about 10 seconds, add in the sausage pieces.
Then add in the sliced onion and mushrooms. Season with a few pinches of salt.
Stir-fry until onions and mushrooms start to get a slight browning. Then pile them to one side.
Now, place the sausages near the middle of the frying pan. Let them cook until their casing starts to pop and burst open.
Then bring everything back together and stir-fry. Turn off heat. Finish with a few cracks of black pepper.