Melt butter over medium heat in a saucepan.

Add sliced mushrooms, salt, black pepper, and oregano.

Sauté, stirring occasionally, until mushrooms are soft and browned, about 10 minutes.

Add flour and mushroom soup mix. Mix to incorporate.

Add milk, half a cup at a time, stirring frequently as sauce thickens.

Taste and add additional seasoning if needed.

Pour mushroom sauce over pasta. Toss to coat and enjoy!