How to Make It
In a large saucepot of salted boiling water, cook the orzo until al dente. Drain and reserve 1 cup of the pasta cooking liquid. Transfer the orzo to a large bowl, coat lightly with olive oil and set aside.
In a large skillet, heat the olive oil over medium heat. Add the garlic and cook for 1 minute, until softened and lightly browned.
Add the pumpkin puree, chili garlic sauce, mustard, nutmeg, and salt and stir to combine. Pour in the reserved pasta water and simmer on medium heat for about 5 minutes. Add the grated cheddar to the sauce, stirring until evenly incorporated and melted, about 3 minutes.
Pour the pumpkin-cheddar sauce over the bowl of orzo and fold it in gently to combine. Toss in the arugula leaves and pepita seeds. Transfer the pasta to plates, drizzle lightly with olive oil, and serve warm.