Peel the potatoes and cut into ½-inch cubes. Boil in salted water until just tender, about 8-10 minutes. After the potatoes have cooked for about 7 minutes, add the peas. Drain and chill until very cold, at least two hours.
While the potatoes and peas chill, cut the tops off of the tomatoes and scoop out the seeds and pulp. Season with salt and arrange tomatoes cut side down on paper towels to drain well.
After the potatoes and peas have chilled, sprinkle with sherry vinegar and season with salt and pepper. Add piquillo pepper, onion and scallions. Gently stir the alioli or mayonnaise into the vegetables.
Fill the tomatoes with the potato salad. Sprinkle with the smoked paprika and garnish with parsley.
Alternatively, drain the ventresca tuna, reserving the oil. Gently flake the tuna and mix with chopped hard-boiled egg. Spoon the tuna and egg mixture over the stuffed tomatoes and drizzle with a little of the reserved oil. Sprinkle the smoked paprika and parsley over top.
Serve chilled with picos breadsticks and cracked olives.