01 - Preheat oven to 425°F and line a baking sheet with parchment paper.
02 - Wash, core, and seed the bell peppers. Slice into 1/2-inch strips.
03 - In a large bowl, combine sliced peppers, red onion, and minced garlic. Drizzle with olive oil, then sprinkle with smoked paprika, salt, black pepper, and chili flakes. Toss to coat evenly.
04 - Spread the mixture in a single layer on the prepared baking sheet.
05 - Roast for 25-30 minutes, stirring once halfway through, until peppers are tender and slightly charred around edges.
06 - Remove from oven. While still warm, drizzle with balsamic vinegar and toss gently.
07 - Transfer to serving platter. Sprinkle with chopped parsley and capers if desired. Serve warm or at room temperature.