To roast the peppers--cut them in half and remove seeds and filaments. Toss with a light coating of olive oil. If doing on the outside grill, roast over medium-high heat, skin side down, until the skin begins to blister and the skin begins to scorch. Remove and cool completely. In the oven, place skin side up and roast at 400F/200C for about 10 minutes or until skin blisters and begins to scorch. Air fryer--same as conventional oven. When cool, roughly dice.
Heat the 2 tablespoons of olive oil in a skillet over medium heat. Add the onion and cook until caramelized; about 10 minutes. Transfer to a bowl (oil and all) then add remaining ingredients.
Serve warm or cold.
Store-bought roasted red peppers may be substituted for your homemade.