Preheat oven to 425 degrees. Toss onions, bell peppers, and garlic with olive oil, salt, pepper and paprika. Roast for 10 minutes.
While onions and peppers are cooking, slice sausages hasselback style. Use a small sharp knife to cut even slices about halfway down into sausage. Do not cut all the way through. In a small bowl, whisk together honey and mustard.
Top onions and peppers with sausage and brush sausage with honey mustard mixture. Roast for 10 minutes, then brush with honey mustard again. Roast for 10 more minutes, and brush with honey mustard for the 3rd time. Return to the oven for an additional 5 minutes if needed. Serve with extra honey mustard and top with fresh parsley.