Adjust oven rack to middle position and heat oven to 350 degrees.
Pulse bread in food processor to coarse crumbs. Spread crumbs on rimmed baking sheet and bake until golden brown and dry, 10-12 minutes. Set aside to cool.
Toss cucumber and 1/2 teaspoon salt in colander and drain for 15 minutes.
Combine cucumber, 3/4 cup yogurt, 2 tablespoons scallions and 1 tablespoon cilantro in bowl and set aside.
Whisk eggs, 2 tablespoons oil, garam masala and 1/4 teaspoon salt in bowl.
Place chickpeas in a large bowl and mash them with a potato masher until mostly smooth. Stir in breadcrumbs, egg mixture, and remaining yogurt, scallions, and cilantro. Form into six 1-inch-thick patties.
Heat 1 tablespoon oil in non-stick skillet over medium heat until shimmering. Add three patties and cook until browned, 4 to 5 minutes per side. Transfer to plate and tent loosely with foil. Repeat with remaining oil and patties.