Preheat oven to 400°F (200°C) and line a baking sheet with parchment paper.
Chop the broccoli, bell pepper, and zucchini into bite-sized pieces.
Toss the vegetables with 0.5 tbsp of olive oil, sea salt, and black pepper on the prepared baking sheet.
Roast the vegetables for 18-20 minutes until tender and slightly charred at the edges.
While vegetables roast, heat the remaining 0.5 tbsp of olive oil in a large non-stick skillet over medium-high heat.
Add the sliced seitan to the skillet and season with garlic powder and smoked paprika.
Sear the seitan for 5-7 minutes, turning occasionally, until the edges are golden and crispy.
Pour the tamari over the seitan in the last minute of cooking, stirring to coat, then combine with the roasted vegetables and serve.