Heat the oven to 350 degrees. Cut the bread into 1-inch cubes and pulse in a food processor in batches to make coarse, soft crumbs. (It should yield about 3 cups.)
Toss the crumbs with the olive oil and spread on a baking sheet. Bake, stirring often, until the crumbs are crisp and barely browned, about 15 minutes.
Put the baked crumbs in a bowl and add the garlic, parsley, thyme, rosemary, and Parmesan.
Season with salt and black pepper and toss well. Set aside.
Cut the peppers lengthwise in half and remove the cores and seeds. Place skin side down in a shallow baking dish in one layer. Season lightly with salt. Fill each pepper half with about 3 tablespoons crumbled feta and press in the cheese with your fingers. With a spoon, divide the seasoned crumbs evenly among the pepper halves.
Bake for about 30 minutes, until the crumbs are golden and the cheese is softened. Serve warm from the baking dish.