Preheat oven to 400º F
In a large shallow wide bowl, combine the peppers with a drizzle of olive oil and a pinch of salt. Toss and coat them with the oil. Arrange them in a single layer on a baking sheet lined with parchment paper. Roast the peppers, rotating the baking sheet halfway through the roasting time, for 30-40 minutes, or until skins have started to blister and pull away from the flesh. Remove from the oven, place in a large bowl and cover tightly with plastic wrap.
When peppers are cool enough to handle, peel the skin off the peppers. Tear the peppers into 1/2 inch wide pieces, discarding the stem, seeds, and membrane.
In a large pot, heat 1/2 cup olive oil over medium heat. Dry the capers with a paper towel and add them to the hot oil. Fry for about 1 minute or until they puff and are crispy. Stir in the tomato paste and cook for about 2 minutes. Add the onion, fennel, chile flakes, 1/2 teaspoon salt and cook for about 5 minutes, stirring now and then until vegetables are tender.
Add the vinegar to the pan, deglazing any browned bits from the bottom. Stir in the peppers and cook for a few minutes, adjust seasoning by adding more salt or vinegar.
Peppers can be served warm, at room temperature or cooled completely and stored in a canning container in the refrigerator for up to 2 weeks.