Preheat your oven to 400°F and line a large baking sheet with parchment paper.
Chop the broccoli into bite-sized florets, slice the red bell pepper into thin strips, and cut the red onion into small wedges.
Place the vegetables on the baking sheet and toss with half of the avocado oil, sea salt, and black pepper.
Roast the vegetables in the oven for 15 to 20 minutes until they are tender and show slight charred edges.
While the vegetables roast, slice the seitan into 1/4-inch thick strips and pat them dry with a paper towel to ensure maximum crispiness.
Heat the remaining avocado oil in a large cast-iron or stainless steel skillet over medium-high heat.
Add the seitan strips to the skillet in a single layer, searing for 3 to 4 minutes per side until a deep golden-brown crust forms.
Mince the garlic and finely grate the fresh ginger, then add them to the skillet for the final 60 seconds of searing.
Drizzle the tamari over the seitan strips, tossing quickly to coat them in the savory glaze before removing from heat.
Plate the crispy seitan alongside the roasted vegetables and serve immediately.