In a medium bowl, whisk together the vital wheat gluten, nutritional yeast, garlic powder, and onion powder until well combined.
Pour in the vegetable broth and stir until a firm dough forms, then knead the dough by hand for about 2 minutes to develop the gluten texture.
Cut the dough into bite-sized pieces and steam them in a steamer basket over boiling water for 15 minutes until firm and chewy.
While the seitan steams, mince the garlic and grate the fresh ginger.
Heat the toasted sesame oil in a large skillet over medium-high heat, then add the steamed seitan pieces, broccoli florets, and sliced red bell pepper.
Sauté for 5 to 7 minutes, stirring frequently, until the vegetables are crisp-tender and the seitan is lightly golden on the edges.
Add the tamari, minced garlic, and grated ginger to the skillet, tossing everything for 1 minute until the sauce is fragrant and coats the ingredients.
Transfer the mixture to a bowl and garnish with sliced avocado and a sprinkle of sesame seeds before serving.