How to Make It
Preheat the oven to 425°. Line a baking sheet with aluminum foil. Rub the cut sides of the squash with 1 tablespoon of the canola oil and season with salt and pepper. Set the squash cut side down on the prepared sheet and roast for about 45 minutes, until tender and caramelized. Scoop out the squash in 4 large pieces and transfer to serving plates; keep warm.
Meanwhile, in a small saucepan of boiling water, cook the quinoa until tender, about 10 minutes. Drain, then return to the saucepan. Cover and let steam for 10 minutes. Scrape the quinoa onto a baking sheet in an even layer and let cool to room temperature.
Reduce the oven temperature to 375°. Drizzle the cooled quinoa with 1 tablespoon of the oil and season with salt and pepper; toss to coat and spread in an even layer. Toast in the oven for about 15 minutes, until golden and crisp. Let the quinoa cool completely.
In a small saucepan, combine the tamarind pulp with 1/4 cup of water and cook over low heat, mashing the tamarind until it breaks down and dissolves, about 2 minutes. Strain the tamarind through a fine sieve, pushing on the seeds; discard the solids.
In a small skillet, heat the remaining 1 tablespoon of oil. Add the garlic, chile and annatto and cook over moderate heat, stirring, until fragrant, 1 minute. Add the tamarind, sugar and 1/2 cup of water and cook, stirring, until thickened to a glaze, about 3 minutes. Stir in 1/2 tablespoon of the lime juice and season with salt.
In a small bowl, toss the arugula with the remaining 1/2 tablespoon of lime juice and season with salt. Spoon some of the tamarind glaze over the squash and top with the crispy quinoa. Garnish with the arugula and serve.