Bring a pot of water to a boil. Slice the tops off the peppers and cut the tops into 1/4-inch dice; discard the cores and stems. Boil the hollowed out peppers until just tender, 4 minutes. Using tongs, carefully transfer the peppers to paper towels to drain, cut side down. Reserve 1 1/2 cups of the cooking water.
In a saucepan, melt 1 tablespoon of the butter. Add the shallots and garlic, season with salt and cook over moderate heat until softened, 3 minutes. Add the rice and cook, stirring, until toasted, 4 minutes. Stir in the coconut milk, ginger, curry paste and the 1 1/2 cups of reserved pepper water and bring to a simmer. Cover and cook over low heat until the liquid is absorbed, 25 minutes.
Meanwhile, preheat the oven to 350°. In a large skillet, heat the remaining 1 tablespoon of butter. Add the diced bell pepper tops and the jalapeño and cook over moderate heat, stirring, until tender, 5 minutes. Add the mushrooms, cover and cook, stirring a few times, until tender, 5 minutes. Uncover and cook, stirring, until the mushrooms are browned, 4 minutes longer. Add the spinach and cook, stirring, until wilted, 1 minute.
Add the vegetable mixture to the rice and stir in the basil and lemon juice. Season with salt. Fill the peppers with the rice mixture and set them in a shallow glass or ceramic baking dish. Cover with foil and bake for about 45 minutes, until the rice filling is heated through. Garnish with basil leaves and serve.