Since the yogurt and cucumbers in the Tzatziki Sauce need to drain for 30 minutes, start making the sauce before the patties. To substitute beef for the lamb, use 80-percent lean ground chuck, decrease the amount of lemon juice to 1 tablespoon and increase the oregano to 2 tablespoons, garlic to 3 cloves, and oil to 1 tablespoon. The test kitchen prefers the flavor of fresh oregano, but 1 teaspoon of dried can be substituted. The skillet may appear crowded when you begin cooking the patties, but they will shrink slightly as they cook. If using pocketless pitas, heat them in a single layer on a baking sheet in a 350-degree oven for 5 minutes. Do not cut top quarters off pocketless pitas; instead, use a portion of a fifth pita to create crumbs in step 1. When cooking the patties, use a splatter screen to keep the mess to a minimum. The patties can be prepared through step 1 and refrigerated for up to a day or frozen before cooking as directed in step 2 (frozen patties should be thawed in refrigerator prior to cooking). This recipe can be doubled.

Directions
1. Adjust oven rack to middle position and heat oven to 350 degrees. Cut top quarter off each pita bread. Tear quarters into 1-inch pieces. (You should have 3/4 cup pita pieces.) Stack pitas and tightly wrap with aluminum foil. Process onion, lemon juice, salt, pepper, oregano, garlic, and pita bread pieces in food processor until smooth paste forms, about 30 seconds. Transfer onion mixture to large bowl; add lamb and gently mix with hands until thoroughly combined. Divide mixture into 12 equal pieces and roll into balls. Gently flatten balls into round disks, about 1/2 inch thick and 2 1/2 inches in diameter.

2. Place foil-wrapped pitas directly on oven rack and heat for 10 minutes. Meanwhile, heat oil in 12-inch nonstick skillet over medium-high heat until just smoking. Add patties and cook until well browned and crust forms, 3 to 4 minutes. Flip patties, reduce heat to medium, and cook until well browned and crust forms on second side, about 5 minutes longer. Transfer patties to paper towel–lined plate.

3. Using a soup spoon, spread 1/4 cup Tzatziki Sauce inside each pita. Divide patties evenly among pitas; top each sandwich with tomato slices, 1/2 cup shredded lettuce, and 2 tablespoons feta. Serve immediately.

Tzatziki Sauce
Makes about 1 cup
Although we prefer the richness of plain whole-milk yogurt, low-fat yogurt can be substituted. Greek yogurt can also be substituted, but use 1/2 cup and skip the step of draining. While we didn't like the flavor of dried mint, dried dill may be used in place of fresh, but reduce the amount to 1/2 teaspoon.

1. Line fine-mesh strainer set over deep container or bowl with 3 paper coffee filters or triple layer of paper towels. Spoon yogurt into lined strainer, cover, and refrigerate for 30 minutes.

2. Meanwhile, combine cucumber, 1/8 teaspoon salt, and lemon juice in colander set over bowl and let stand 30 minutes.

3. Discard drained liquid from yogurt. Combine thickened yogurt, drained cucumber, remaining 1/4 teaspoon salt, garlic, and mint in clean bowl.