Pulse the bread in a food processor until coarsely chopped. Heat 2 tablespoons olive oil in a medium skillet over medium heat. Add the bread, 1 teaspoon rosemary, the red pepper flakes and a pinch of salt. Cook, stirring occasionally, until the bread is golden brown, about 10 minutes; transfer to a bowl.
Meanwhile, bring a large pot of salted water to a boil. Add the green beans and cook until crisp-tender, about 6 minutes. Drain, rinse under cold water and blot dry with paper towels. (You can refrigerate the green beans, covered, for up to 4 hours; keep the bread mixture at room temperature.)
Heat the remaining 1/4 cup olive oil and the garlic in a large nonstick skillet over medium-high heat. Cook until the garlic is lightly golden, about 3 minutes, adding the remaining 1 teaspoon rosemary during the last 30 seconds. Add the green beans and lemon zest; cook, stirring, until coated. Season with salt and pepper and stir in the bread mixture.