In a large saucepan, cover the lima beans with 2 inches of water and bring to a boil. Simmer over low heat, stirring occasionally, until the limas are just tender but still al dente, about 2 1/2 hours; add water as needed to keep the limas covered by 2 inches. Season the limas with salt and let stand at room temperature for 5 minutes. Drain the limas, reserving 1 1/2 cups of the cooking liquid.

In a medium saucepan, heat 3 tablespoons of the olive oil. Add the onion and garlic and cook over moderately low heat until softened, about 8 minutes. Add the tomatoes, oregano and the reserved bean cooking liquid and simmer over low heat, stirring occasionally, until the sauce has reduced to 1 1/2 cups, about 1 hour. Season the tomato sauce with salt.

In a mini food processor, combine the olive oil with the oregano, parsley and garlic and pulse to a coarse puree. Season the oregano pesto with salt.

Preheat the oven to 425°. In a 9-by-13-inch baking dish, mix the limas with the tomato sauce and sprinkle the feta on top. Bake in the upper third of the oven for about 40 minutes, until the beans are bubbling and the cheese is browned. Remove the baking dish from the oven and let stand for 10 minutes.

Meanwhile, in a large skillet, heat the remaining 2 tablespoons of olive oil. Add the bread crumbs and cook over moderately high heat, stirring, until toasted, about 3 minutes. Season with salt.

Top the beans with the bread crumbs, dollop with the oregano pesto and serve.