To make the dressing, combine the sumac, lemon juice, and pomegranate molasses in a small jar with a lid. Use a Microplane to grate the garlic clove right into the jar. Add the sherry vinegar, salt, and pepper, cover the jar and shake well. Pour in the olive oil and cover and shake again until the dressing is emulsified. Set aside.
Make the croutons. Line a baking sheet with parchment paper. Preheat the oven to 325°F. In a medium bowl, use your hands to toss the bagel coins with the olive oil and salt. Scatter the bagel coins across the parchment. Bake for 8 minutes, until crisp and slightly golden. Remove from the oven and sprinkle with za’atar. Let cool.
Make the salad. Set a colander over a catch bowl. Chop the tomato into 1-inch dice, place in the colander, and add the salt. Toss well and allow the tomatoes to exude excess liquids for about 10 minutes.
Line a wide, shallow bowl with the lettuce, torn into bite-sized pieces.
If the cucumber is very fresh and thin-skinned, use a table fork to scrape vertical lines down the length of the cucumber. Cut the cucumber in half lengthwise and make half-moon-shaped, 1/4-inch pieces with a decorative edge. If the cucumber has thick, bitter skin, peel before slicing. Add the prepared cucumber to the salad bowl.
Scatter the scallion, parsley, cilantro, and mint over the lettuce and cucumber. Then gather the tomatoes in your hands leaving any excess moisture behind and place the tomatoes on top of the salad. Crumble the feta over the top, scatter the bagel chips everywhere.
Shake the dressing again and pour it evenly across all of the ingredients. Mix the salad together (use your impeccably clean hands!) and let it rest for about 10 minutes so all of the flavors combine. Toss it once more and serve. Make sure every serving includes a spoonful of the juicy bits in the bottom of the bowl.