Prep the sprouts. Preheat the oven to 425°F (218°C). Wash the sprouts and remove any browned or tough outer layers. Cut the sprouts in half (if any sprouts are large, cut into quarters).
Roast the sprouts. Spread the sprouts out on a baking sheet and drizzle with the oil. Season generously with salt and pepper and toss to coat with your hands. Roast for 30 to 35 minutes, tossing after 20 minutes, until the sprouts are nicely browned. If your sprouts are quite small, flip after 15 minutes and roast for 30 minutes.
Meanwhile make the Sweet Chili sauce. Whisk together the tamari or soy sauce, agave, water, sriracha, sesame oil, and rice vinegar in a small bowl until well combined.
Sauté the aromatics. Just before the sprouts are done roasting (or after they’re done roasting), heat the 2 teaspoons oil in a medium frying pan over medium-high heat. Add the scallions, garlic, and ginger and cook, stirring often until golden, about 2 minutes.
Meanwhile, make cornstarch slurry: whisk together the cornstarch and 2 tablespoons water until smooth and. no longer clumpy.
Add the Sweet Chili Sauce to the frying pan and bring to a simmer. Then add the cornstarch slurry, stir well, and simmer until the sauce has thickened, 2 to 3 minutes.
Toss in the roasted sprouts and coat in the sauce. Sprinkle with sliced green scallion tops, roasted cashews (if using), and sesame seeds.