Step 1

In a large bowl, cover the dried beans with 2 inches of water and let them soak overnight. Drain and rinse the beans, then transfer them to a medium enameled cast-iron casserole. Add 3 quarts of the water and bring to a simmer over moderate heat, skimming as necessary to remove the foam that rises to the surface. Cook the beans over low heat until almost tender, about 1 hour. Add the tomatoes, garlic, celery leaves, oregano and 1/4 cup of the olive oil. Season with salt. Continue cooking until the beans are very tender, about 1 1/2 hours longer.

Step 2

Meanwhile, in a large skillet, heat the remaining 1/4 cup of olive oil. Add the onion and cook over low heat until softened but not browned, about 8 minutes. Add the squash and the remaining 1 cup of water, cover and simmer over low heat until the squash is just tender, about 10 minutes.

Step 3

When the beans are done, stir in the squash. Season with salt and crushed red pepper and simmer for 5 minutes. Serve in shallow soup bowls.