Mince garlic and zest lemon. Reserve lemon for another use. Combine garlic and lemon zest with spice blend, oil, and salt.
Remove stems from mushrooms and quickly rinse, removing any dirt. Rub mushrooms with marinade and set aside for 20-30 minutes.
Crumble feta cheese and dice tomato. Mince parsley. Combine together, reserving a small amount of parsley for garnish.
Grill mushrooms over high heat*, gill side down for 3-5 minutes. Turn over and sprinkle/press feta cheese-tomato filling onto top of mushrooms. (If you need to remove from grill to do this, that is fine). Grill until cheese is melt-y and mushrooms are soft. Garnish with parsley.
*Mushrooms may also be cooked under broiler. Place on a baking sheet, gill side up, and fill with feta cheese/tomato filling. Cook under broiler until cheese is browning and mushrooms are soft.