Step 1

Preheat oven to 350F.

Step 2

Bring a large pot of salted water to a boil over medium high heat. Add spaghetti and one tablespoon olive oil. Cook until al dente (fully cooked but still firm), about 10 minutes or according to package directions. Drain the noodles in a colander and rinse under cold water to stop the cooking process and cool down. Set aside in the pot.

Step 3

Heat remaining 2 tablespoons olive oil in a large saucepan for 2 minutes over medium high heat, until the hot oil sizzles. Add mushrooms and sauté until golden brown, about 4-5 minutes.

Step 4

Stir in onion and garlic, and sauté until fragrant, about 2 minutes. Add salt, pepper and flour. Stir well to combine, about 1 minute.

Step 5

Pour in chicken broth and lemon juice and whisk until the sauce is smooth and uniform. The sauce might be a little bit clumpy in the beginning.

Step 6

Whisk in heavy cream and bring the sauce to a simmer over medium heat. Let it simmer and stir occasionally until thickened, about 5-10 minutes. The sauce should be similar to in consistency to gravy and thick enough to coat the back of a spoon. Remove from heat and stir in spinach until wilted, about 1 minute.

Step 7

Add in cooked spaghetti and shredded turkey. Toss well until fully combined and coated.

Step 8

Transfer the mixture into a 9x13 casserole pan and evenly top with mozzarella cheese.

Step 9

Lightly grease a large piece of aluminum foil and cover the pan. Greasing the foil prevents the melted cheese from sticking to the foil while baking.

Step 10

Bake the tetrazzini covered for 25 minutes.  Then, remove the foil and bake uncovered for another 15 minutes or until the melted cheese turns golden brown and bubbly. Optionally, turn on broiler on high and broil for 3-4 minutes to brown the cheesy crust and get it crispy.

Step 11

Let the tetrazzini rest for 10 minutes before serving. This is to ensure the cream sauce sets a bit and is not too runny.