Heat oil in a large skillet over medium-high heat.Add the cut sausages to the skillet and brown on both sides, 2-3 minutes per side. Transfer brown sausages to a plate and set aside. Add the sliced bell peppers and onions to the skillet with some salt and pepper and cook, stirring, until tender, 4 to 6 minutes. Pour in the marinara and stir to combine. Nestle the sausages into the sauce and let simmer to reheat the sausages, about 3 more minutes. Serve over a bed of arugula, enjoy!