Torta de Calabacitas

Name: Torta de Calabacitas
Ingredients: 6 tablespoons vegetable oil; 1 1/2 medium onions, thinly sliced; 8 poblano chiles, roasted, peeled (see Note), and cut into 1/2 x I 1/2-inch strips; 2 pounds plum tomatoes, peeled, seeded, and coarsely chopped; I teaspoon salt; 1 1/2 pounds small zucchini, cut into 1/8-inch slices; Salt and freshly ground black pepper; 2 tablespoon dry bread crumbs; 3 large eggs, separated; 6 ounces thinly sliced feta cheese, crumbled; 3 tablespoons unsalted butter, at room temperature