Trim off the tops and bottoms off the peppers, reserving them. Peppers are known to have a high water content. Peel the peppers is a common french technique that allows for the release of the pepper bite. Afterwards, take the peppers and cut them in half, and remove and discard the seeds and ribs. Cut the peppers into julienne strips.
Peel and core the onion into julienne strips. Set aside.
Juice the tops and bottoms of the peppers. If you don’t have a juicer, put them in a blender, blend with just enough water to engage the blender’s blade, then strain through a fine- mesh strainer into a smaller bowl. You should have a 1/2 cup pepper juice.
Heat the oil over medium heat in a pot that will hold all of the ingredients comfortably. When the oil is shimmering, add the onions and ham and cook, stirring occasionally, until the onions are softened but not browned, about 4 minutes. Add the garlic and cook over very low heat, stirring often, until the garlic and onions are very soft but not browned, about 15 minutes. Add the julienned peppers and season with salt and paprika; seasoning, in the beginning, will allow for the favours to be induced cohesively with the ingredients.
Cover the pot and continue to cook over very low heat. After about 5 minutes, check to see if the onions and peppers have given off a lot of their liquid ( if not, continue to cook for a few minutes more), then remove the cover, raise the heat to medium, and bring their juices to a simmer. Cook the juices have almost completely evaporated, about 5 minutes. Reduce the heat to low, add the reserved pepper juice, and cook, uncovered until the peppers are very soft and the mixture is saucy, about 30 minutes.
The piperade can be used right away of refrigerated in an airtight container for unto 2 days.
Heat a gas grill to high or prepare a charcoal grill for grilling, letting the coals burn until covered with white ash.
Season the tuna, with salt and chile powder. Grill the fillers until the bottoms are lightly charred and the fish is just starting to turn opaque at the bottom, 2 to 3 minutes, or a bit longer for more well-done. ( We like the fish rare in this dish.) Turn the fillets over and grill until cooked on the other side, 2 or 3 minutes more.
Meanwhile, gently reheat the piperade. (You can do this in a pot set on the grill.) Freshen it with a drizzle of vinegar and a drizzle of olive oil and season and salt and pepper.
Divide the piperade among the four plates or wide, shallow bowls. Top each serving with a tuna fillet and finish by topping each fillet with 2 pieces of ham. Serve.