Heat a large wok or pot over high heat. Open a can of coconut milk, and scoop out ¼ cup of the cream from the top. Put the cream into the wok, and also add the curry paste. Cook and reduce this mixture until it resembles the consistency of smooth peanut butter. Add in the onion, red pepper, and extra fresh chili if using, cooking to soften slightly, about 1-2 minutes. Toss in the squash, chickpeas, basil, tamarind paste, sugar, soy sauce, salt, and remaining coconut milk, mixing to combine.