Place the top oven rack in the center position, place a 10 inch cast iron skillet in the middle and pre-heat the oven to 400ºF.
Carefully remove the hot skillet from the oven.
Add the olive oil and gently swirl the pan to coat the bottom with the oil. Arrange the sausages, red onion, garlic cloves, and tomatoes in the skillet. Season with the Italian seasoning and a generous amount of salt and black pepper, to taste.
Return the skillet to the oven and roast for 20-25 minutes.
Remove from oven and add the white beans and red wine vinegar to the skillet and gently stir to combine. Flip the sausages over for even browning
Return to the oven and roast until sausages are brown, about 10-15 minutes.
Remove the skillet from the oven and remove the whole garlic cloves. Peel, then smash the roasted garlic with the flat end of a table knife and add back to the pan with the fresh basil. Stir to combine and serve immediately.