Put a sauté pan over a medium-high flame and heat the oil.
Add in the peppers and cook until they begin to soften, about 15 minutes. Lightly salt the peppers.
Add the garlic and mushrooms to the pan and cook until the mushrooms have released some of their water, about 5-7 minutes.
Lightly salt again.
Add in the butter and toss until melted.Taste for seasoning and season with more salt and fresh black pepper as desired.