1. Wash the spinach with your hands and then squeeze the water out of it about 5 times, hard.
2. Dry the spinach even more in a paper towel by squeezing the juice out.
3. Chop the portobello mushrooms, starting at the top of the dome, slicing down to the bottom of the stub. Slice each one into about 8 or 9 thin slices.
4. Push about 1/3 of the spinach into the bottom of the pita pocket with about a third of the mushrooms and half the walnuts; and then top that with most of the cheese, pushing down to make room for the rest.
5. Put the rest of the spinach, walnuts, and mushrooms in the pocket and then the rest of the cheese.
6. Microwave on high for about 20 seconds.
7. Pour the olive oil into a medium hot skillet and rub one half the pocket in the oil, and flip it so that the oiled part is on the top.
8. Fry the pocket for 30 seconds to a minute on each side.2.