Cook the sausages in a large skillet over medium heat.
Remove the sausages and set them aside.
Add olive oil to the skillet and sauté the onions and garlic.
Add sliced bell peppers to the skillet.
Stir in the diced tomatoes and Italian seasoning.
Return the sausages to the skillet, slicing them into bite-sized pieces.
Season with salt and pepper to taste.
Meanwhile, bring a pot of salted water to a boil for the potatoes.
Cook the peeled and chopped potatoes until tender.
Drain the potatoes and return them to the pot.
Add butter and milk, mashing until smooth.
Serve the sausage and peppers over the mashed potatoes.