Slice or chop your portobellos to your liking, making sure to make them all similar sizes, you can pull the stems apart and use them as well. Sprinkle with a generous amount of gyro spice and about a teaspoon or so of fresh mint and set aside.
Heat a pan with cooking oil over medium heat cook your portobellos until fragrant and starting to brown, remove from the pan and keep warm, toss your pita bread in the same pan and toast.
When ready to assemble the pita, layer portobellos on the bottom, followed by lettuce, tomatoes, onion, and yogurt sauce. Enjoy!