Preheat and Prepare: Position a rack in the center of your oven and preheat to 400°F (200°C). In a large 9x13 inch baking dish, combine the cubed potatoes, chopped bell peppers, sliced red onion, and chickpeas. Drizzle with 3 tablespoons of the extra virgin olive oil, season with 1/4 tsp of the salt and all of the black pepper, and toss to coat.
Par-Roast Vegetables: Place the baking dish in the oven and roast for 20 minutes, stirring once halfway through. This gives the vegetables a head start to become tender.
Hydrate the Binder: While the vegetables roast, combine the whole-wheat panko, grated yellow onion, and minced garlic in a large mixing bowl.
Form the Polpettes: To the panko mixture, add the ground chicken, grated zucchini, egg, parsley and mint, lemon zest, dried oregano, smoked paprika, cumin, and the remaining 1/4 tsp of salt. Gently mix with your hands until just combined, being careful not to overwork the mixture. Form into approximately 24 golf ball-sized meatballs.
Combine and Roast: After 20 minutes, carefully remove the baking dish from the oven. Nestle the polpettes among the partially roasted vegetables.
Make the Vinaigrette: In a small bowl, whisk together the remaining extra virgin olive oil, fresh lemon juice, Dijon mustard, and fresh (or dried) oregano until emulsified.
Final Bake: Drizzle about half of the vinaigrette over the polpettes and vegetables. Return the dish to the oven and bake for an additional 20-25 minutes, or until the polpettes are cooked through to an internal temperature of 165°F (74°C). For extra browning, you can broil for the last 1-2 minutes, watching carefully.
Dress and Serve: Remove the dish from the oven. Drizzle the remaining vinaigrette over everything, garnish with fresh parsley or mint, and serve immediately.