Preheat a grill or grill pan to medium high. Combine the turkey, minced onion, garlic, coriander, chili powder, 1 teaspoon salt and a few grinds of pepper in a large bowl. Form into four 4-inch-square patties. Transfer to a baking sheet and refrigerate until ready to grill.
Meanwhile, spread the eggplant on a paper towel–lined baking sheet. Sprinkle with salt and set aside 10 minutes, then pat dry.
Brush the eggplant with the olive oil and oil the grill grates. Grill the eggplant until tender and well marked, 4 to 5 minutes per side. Meanwhile, grill the turkey patties until marked and cooked through, 2 to 3 minutes per side.
Fill the pitas with the lettuce, a few eggplant slices, a turkey patty and the sliced onion. Thin the hummus with 3 tablespoons water, then spoon into the pitas. Serve with vegetable chips.