1. Heat the oil in a large skillet over medium heat. Add the bell peppers and onion and cover. Cook, stirring occasionally, until the vegetables begin to soften, about 3 minutes. Uncover and reduce the heat to medium-low. Cook, stirring occasionally, until the peppers are very tender but hold their shape, about 30 minutes.

2. Stir in the garlic, oregano, and hot red pepper and cook until the garlic gives off its aroma, about 1 minute. Stir in the capers, vinegar, and sugar and cook for 1 minute to blend the flavors. Season to taste with salt. Cool completely. (The peperonata can be prepared up to 1 week ahead, cooled, covered, and refrigerated.) Serve at room temperature.