Cook fettuccine according to package directions.
In the meantime, heat olive oil and butter in a large skillet.
Add onions and mushrooms; cook over medium heat until tender, stirring occasionally.
Stir in garlic and continue to cook for 1 minute.
In a small bowl whisk together flour and broth.
Add to skillet.
Stir in the milk and vegetables.
Season with salt and pepper, increase heat and bring mixture to a boil.
Continue to cook and stir for 1 minute or until sauce has thickened.
Decrease heat to medium-high and add turkey; cook for 3 to 4 minutes, stirring occasionally, until heated through.
Remove from heat.
Serve over prepared fettuccine.