Red Lentil and Squash Sambar

I made this out of Meera Sodha's new cookbook, Fresh from India, which I love the look of, and if this recipe is any indication, I am going to also love the results.  The original calls for eggplant, but since in my hemisphere, squash and eggplant are not overlapping seasons, I made it with squash, and will try it again next summer with eggplant instead.  The melding of the sweetness of the squash with the sour of the tamarind is delicious, and it is hearty because of the lentils.

• 1 cup red lentils
• 4 tablespoons canola oil, divided
• 1/2 teaspoon fenugreek seeds
• 2 teaspoons coriander seeds
• 1 1/2 teaspoons cumin seeds
• 3/4 teaspoon black mustard seeds
• 12 fresh curry leaves
• 4 shallots, finely sliced
• 8-16 ounces butternut squash, cut into 1-inch cubes
• 4 medium, ripe tomatoes, chopped
• 1 1/2 teaspoons sugar
• 2 teaspoons tamarind paste
• 1 1/2 teaspoons nice red chili powder
• 7 ounces green beans, trimmed

1. Wash the lentils with cold water until the water runs clear, then put into a deep saucepan, cover with three times the amount of water, and bring to the boil. Simmer for 25 minutes, or until soft, scooping off any foam.
2. Meanwhile, put 1 tablespoon of oil into a wide, lidded frying pan and add the fenugreek, coriander, and cumin seeds. Stir-fry for a minute, then take off the heat and grind to a coarse paste with a pestle and mortar.
3. Put the remaining oil into the frying pan over a medium-high heat. When hot, add the mustard seeds and curry leaves, followed closely by the shallots, and cook for around 10 minutes, until the shallots are golden. Then add the diced squash and a couple of tablespoons of water, cover with the lid, and cook for 5 minutes.
4. Add the tomatoes, along with the spices you ground earlier, the salt, sugar, tamarind paste, and chilli powder. Cover again and leave to cook for a further 5 -10 minutes, until the tomatoes have broken down and the squash is tender. Add the lentils to the vegetables (or the other way around, depending on which pan is bigger), then add the green beans and enough water to make a thick, soupy texture, and cook for a final 5 minutes. Taste and adjust the salt, sugar, and tamarind as you wish.