Makes 8+ servings
3 tablespoons extra-virgin olive oil
8 ounces whole wheat bread, cut into 1/2-inch cubes
6 ounces baby spinach, finely chopped
1/2 cup crumbled feta cheese, divided
2 teaspoons Dijon mustard
1/2 teaspoon grated lemon zest
1 tablespoon lemon juice
6 large eggs, beaten
2 cups milk
Kosher salt and freshly ground black pepper
Preheat the oven to 350 degrees. Spread the bread cubes onto a baking sheet. Drizzle the bread cubes with about 1 tablespoon of olive oil and season lightly with salt. Bake until lightly browned. Set aside to cool. Transfer the bread to a large bowl. Stir in the spinach and 1/4 cup of the feta.
In a large bowl, whisk together 2 tablespoons of olive oil, the mustard, lemon zest, and lemon juice. Add the eggs and beat until blended. Add the milk and season with 1 teaspoon of salt and 1/2 teaspoon pepper. Pour the egg mixture over the bread and spinach mixture. Use your hands and toss well to combine.
Transfer the bread mixture to a baking dish or two and let stand at room temperature for 2 hours. Alternately, you can refrigerate the mixture over night.
Sprinkle the remaining feta on the bread pudding and bake in the center of the oven until risen and set, about 40 minutes. Scatter the oregano on top. Cut into squares and serve