Preheat your oven to 400°F (200°C) and line a large baking sheet with parchment paper.
Drain and rinse the chickpeas, then pat them thoroughly dry with a clean kitchen towel to ensure they crisp up in the oven.
Cut the seitan into bite-sized cubes and place them in a large mixing bowl with the chickpeas, broccoli florets, and cauliflower florets.
Drizzle the olive oil over the mixture and sprinkle with sea salt, black pepper, garlic powder, and smoked paprika.
Toss everything together until the vegetables and protein are evenly coated in the oil and spices.
Spread the mixture in a single layer on the prepared baking sheet, ensuring enough space for the air to circulate.
Roast for 20 to 25 minutes, tossing halfway through, until the vegetables are tender-crisp and the seitan edges are golden.
Remove from the oven, drizzle with fresh lemon juice, and sprinkle with nutritional yeast before serving warm.