Rinse peppers under cold water and pat dry. Slice off tops and bottoms, stand upright, and cut down along the inside to remove seeds and white ribs. Slice lengthwise into ½-inch strips; halve crosswise for shorter pieces. Keep sizes uniform so everything cooks evenly. If adding onion, slice it now. Measure out olive oil, salt, and pepper. Have everything ready before the pan goes on — sautéing moves fast.

Heat a large Skillet over medium heat. Add 1 tbsp olive oil per 2 peppers; warm 30–60 seconds until shimmering. Add pepper strips in a single layer — work in batches if crowded. Season with salt and pepper, stir to coat. Cook over medium heat, stirring every 2–3 minutes, for 6–10 minutes. At 6 minutes: slightly softened with snap. At 10 minutes: tender throughout with light color. For very soft peppers, cook 30–40 minutes over medium-low, stirring occasionally. Add garlic halfway through cooking. If browning too fast, add a splash of white wine or water and briefly cover to steam.

In a small Mixing Bowl, combine the 1 ½ tsp smoked paprika, 1 tsp dried thyme, 1 tsp 1 ½ tsp kosher salt divided, and ½ tsp black pepper freshly ground. Rub the 4 pieces bone-in, skin-on chicken thighs patted dry all over with 1 tablespoon of 3 tbsp olive oil divided, then coat evenly with the spice mixture. Set aside.

Add the sliced 1 whole red bell pepper seeded and sliced into strips, 1 medium zucchini sliced into half-moons, about ½-inch thick, and 1 medium red onion cut into wedges wedges to the Baking Sheet. Drizzle with the remaining 2 tablespoons of 3 tbsp olive oil divided and the 1 tbsp balsamic vinegar for drizzling over vegetables. Scatter the 4 cloves garlic minced over the vegetables, season with the remaining ½ tsp 1 ½ tsp kosher salt divided, and toss to coat. Spread into an even layer, leaving space in the center for the chicken.

Remove from the Oven and let the 4 pieces bone-in, skin-on chicken thighs patted dry rest for 5 minutes. Scatter fresh 2 tbsp fresh flat-leaf parsley roughly chopped over the top and serve directly from the pan.