Fill a medium sized pan with water, add the potatoes and about 1 teaspoon of salt, and let it boil. Once boiling, decrease the heat to medium and cook the potatoes for about15 minutes. Then, pass them through cold running water. Transfer the potatoes to a cutting board and when they’re cool enough to handle, cut them into halves. Set aside.
Brush a grilling pan with olive oil and set it on high heat. When it’s hot, but not smoking, add the peppers’ strips, skin side down, seasoned with a pinch of salt. Grill them for 7 to 10 minutes, or until slightly charred – to get visible grilling marks, I like to press down the peppers’ strips with the back of a spoon against the grilling surface. Grill on the other side for about 5 minutes. Transfer the grilled peppers to a plate and set aside.
Add the onion rings (also lightly salted) to the grilling pan and cook them for 3 to 4minutes or until soft and browned.
In a medium sized bowl, combine 3 tablespoons of olive oil with the red wine vinegar. Add a pinch of salt and whisk until incorporated.
Put all the vegetables (onion, peppers’ strips and boiled potatoes) on a large serving plate. Pour the oil and vinegar mixture over them and toss well. Finally, add the capers (if using), minced garlic and coriander on top. Serve immediately.