Whisk AP flour, garlic powder, cayenne pepper and salt in a bowl. Drop seitan and toss around to coat with the flour.
Heat 1 tbsp peanut oil in a pan and sauté seitan on medium-high heat till lightly browned on all sides. Remove and keep aside.
Rinse and wipe the same pan clean; add 1 tbsp peanut oil, sauté on medium-high heat green onions, carrots and peppers along with ginger, garlic and red pepper flakes till tender and browned around the edges, about 8-10 minutes. Keep stirring occasionally to avoid burning.
Now add Chinese broccoli, cover and let the leaves wilt.
In the mean time mix all the ingredients for the sauce to make smooth slurry. Add some water to help mixing.
Slowly stir in the sauce and sautéed seitan into the veggies and cook on medium flame until the sauce thickens, about 5 minutes. Season with salt and pepper and serve over brown rice or noodles.