Slice the bell peppers and onion, and mince the garlic cloves.
In a skillet over medium heat, brown the Italian sausage for about 5 minutes until it is slightly cooked through (optional).
Transfer the sliced bell peppers, onion, and minced garlic to the crockpot.
Add the browned sausage (or raw if you prefer) on top of the vegetables.
Pour the can of diced tomatoes over the sausage and vegetables.
Sprinkle the Italian seasoning, salt, and black pepper over the top.
Drizzle with olive oil and balsamic vinegar, if using.
Stir gently to combine the ingredients, being careful not to break up the sausage too much.
Cover the crockpot and cook on low for 6 to 8 hours, or on high for 3 to 4 hours.
Once cooked, stir again before serving and adjust the seasoning if necessary.