Heat grapeseed oil in a large skillet over medium-low heat. Cook and stir pita bread pieces in hot oil until golden brown, 2 to 3 minutes. Transfer bread pieces to a paper-towel lined plate.

Stir romaine lettuce, tomato, red onion, cucumber, feta cheese, mint, and parsley together in a large bowl.

Whisk olive oil, lemon juice, garlic, Greek seasoning, sumac, salt, and black pepper together in a bowl until completely combined. Pour olive oil mixture and pita bread pieces into lettuce mixture; toss to coat.