Poke each sausage a few times with a paring knife or fork (this helps release steam as they cook).
In a large skillet with a lid, heat olive oil over medium heat. Once hot, add sausages and brown gently and slowly. Cook for 5 minutes, turning occasionally to gently brown on all sides. (They should not be fully cooked.)
Once browned, remove sausages to a plate. Set aside.
Increase heat to high. Add onion and pepper slices. Toss to coat in oil and sear vegetables until slightly blackened, stirring often. Add garlic and cook for 1 more minute.