Prepare all ingredients as listed.
Combine the sliced cucumber and water. Refrigerate while preparing the meal.
Place the potatoes in a saucepan and cover with cold water. Add salt. Bring to a boil, then simmer for 12–15 minutes, until tender but still holding their shape. Drain well.
While the potatoes cook, combine the sliced red onion, red wine vinegar, and dried oregano. Let stand for about 10 minutes.
Add the warm potatoes to the onion mixture. Fold in the cherry tomatoes, olives, capers, and fresh basil. Season with black pepper and drizzle with extra-virgin olive oil. Toss gently and set aside.
Heat the grill on medium-high heat.
Rub the tilapia with the olive oil, then season with oregano, salt, garlic powder, paprika, black pepper, and lemon.
Grill the corn on all sides until tender and lightly charred. Brush with olive oil and season with black pepper.
Grill the fish on both sides, to an internal temperature of 145°F (63°C). Finish with lemon juice if preferred.
Serve the fish with Sicilian potato salad, grilled corn together, watermelon, dates, and cucumber water with ice, if desired .