Preheat the oven to 400°F (or 204°C). Line a baking sheet with parchment paper. Slice the pumpkin in half using a large sharp knife and rocking motion. If it’s too tough to slice, pop it in the microwave for 30 – 60 seconds to slightly soften. Use a large spoon to scoop out the seeds and stringy bits.
Roast the pumpkin. Drizzle the pumpkin halves with a bit of the oil, and season well with salt and pepper. Place the halves, flesh side down, on the lined baking sheet. Roast in the preheated oven for 30-45 minutes, until the flesh is fork tender and lightly browned. Meanwhile, prep the rest of the ingredients.
While the pumpkin is roasting, boil the tofu. Bring a large pot of water to a boil and season with salt. Drain the tofu and pat with paper towels to remove excess water. Chop the tofu into cubes. Add tofu to the boiling water. Once the water returns to a boil, boil for 90 seconds. Use a strainer to remove the tofu from the water and drain immediately, or gently drain over a colander. Set aside.
Once the pumpkin is cool enough to handle, the skin should be easy to peel off. Take one roasted pumpkin half and use a knife to score the flesh into cubes. Set the pumpkin cubes aside. For the other half, scoop out all of the flesh using a spoon and add it to a blender.
Make the Pumpkin Sauce: in the blender with the pumpkin, add 1 cup water, 1 ½ teaspoons kosher salt, and black pepper to taste. Blend until smooth – the texture should be a relatively thick puree. If needed, a bit more water until it comes together.
Cook the aromatics. Heat a deep, large frying pan over medium-low heat. Add the black mustard seeds, cumin seeds, and coriander seeds and toast until fragrant, about 3 to 4 minutes. Turn off the heat and transfer to a mortar and pestle and roughly crush, or grind the spices in a spice grinder. Add these to a bowl with the other ground spices – turmeric, cinnamon, and nutmeg.1. NOTE: if using pre-ground cumin and coriander, just toast the mustard seeds and don’t crush them (leave them in the pan) and move on to step 7.
Heat the same pan over medium-high heat and then add 1 ½ tablespoons of neutral-flavored oil. Once shimmering, add the onions with a pinch of salt and sauté until they just start to turn brown, 4 to 6 minutes. Add the garlic, ginger, green chilies and cook for 1 to 2 minutes, tossing frequently. Add the ground spices—freshly ground or pre-ground cumin and coriander, turmeric, cinnamon, and nutmeg— and cook for 30 seconds, stirring frequently to prevent burning.
Pour in the Pumpkin Sauce and coconut milk, and stir until well combined. If the mixture starts to boil, lower the heat. Add in the roasted reserved pumpkin cubes, green beans, and 1 teaspoon of kosher salt.
Bring to a simmer and cook for 4 to 5 minutes, or until the curry starts to thicken. Add in the boiled tofu and gently simmer for another 3 to 4 minutes, or until the green beans are crisp-tender and the tofu is heated through.
Add the garam masala, lemon juice, and cilantro, and stir to combine. Taste for seasonings and adjust accordingly, adding more salt, lemon juice, or garam masala as needed. Garnish with additional fresh cilantro, if desired.