Cut sausage into chunks. In a large skillet add 1 tablespoon of the olive oil. Over medium heat, cut sausage into chunks and brown. Place into crockpot.
Add the second tablespoon of olive oil to skillet and cook the onion and peppers to your preferred doneness. You don't need to cook them all the way because they will cook in the crockpot.
Add the garlic and cook for about 1 minute.
Add to the crockpot. Pour marinara sauce on top and add the Italian seasoning.
Cook on low for 3-4 hours.
Serve over on plan pasta of choice.