Butterfly the turkey breast by pressing the turkey breast flat on the cutting board with one hand, while slicing into the turkey breast parallel to the cutting board with the other. Slice into the longest side of the turkey breast, but stop before you cut all the way through. You should then be able to open the turkey breast up like a book, making it twice as wide as it was when you started.

Combine the spinach, feta cheese, lemon zest, thyme and toasted walnuts in a bowl. Season with salt and pepper to taste (careful with the salt because feta can be quite salty). Season the turkey with salt and pepper and then spread the mixture across the entire surface of the opened turkey breast, except for 2 inches from the edge of one of the short sides. Roll the turkey breast up, starting from one short side and ending at the short side with the 2 inches of uncovered meat. Tie the turkey breast closed in several places with kitchen twine.

Pre-heat the pressure cooker using the BROWN setting.

Season the turkey breast with salt and freshly ground black pepper. Add the oil to the pressure cooker and brown the turkey breast on all sides. Set the browned turkey breast aside. Scatter the onion and carrots in the cooker. (These vegetables will act like a rack, keeping the turkey off the bottom of the cooker.) Place the browned turkey breast on top. Pour in the chicken stock and wine, and lock the lid in place.

Pressure cook on HIGH for 20 minutes.

Let the pressure release NATURALLY for 15 minutes. Release any residual pressure with the QUICK-RELEASE method and carefully remove the lid. Transfer the turkey breast to a cutting board and let it rest for at least 5 minutes.

While the turkey is resting, make a quick sauce. Combine the flour and butter in small bowl until it forms a paste. Remove and discard the onions and carrots from the braising liquid and return the pressure cooker to the BROWN setting. Whisk the butter-flour mixture into the liquid in the cooker and bring it to a simmer to thicken. Season to taste with salt and freshly ground black pepper and add about 2 tablespoons fresh chopped thyme leaves. Slice the turkey breast and serve with the sauce poured over the top.