Preheat your oven to 400°F (200°C) and line a large baking sheet with parchment paper.
Toss the cubed butternut squash, halved Brussels sprouts, and sliced red bell pepper with half of the olive oil, sea salt, black pepper, and smoked paprika.
Spread the vegetables in a single layer on the baking sheet and roast for 20 to 25 minutes until the squash is tender and the sprouts are browned.
While the vegetables roast, heat the remaining olive oil in a large cast-iron skillet over medium-high heat.
Add the cubed seitan to the skillet and season with garlic powder and tamari, stirring to coat evenly.
Sauté the seitan for 8 to 10 minutes, allowing the edges to become golden-brown and slightly crispy.
Remove the roasted vegetables from the oven and carefully fold them into the skillet with the seitan.
Stir everything together for 1 to 2 minutes to meld the flavors, then serve immediately.