Cook pasta 1 minute less than package directions. Drain very carefully, season with ½-tablespoon olive oil to prevent from sticking, cool down flat on a sheet pan. Store in the fridge in an airtight container.
In a skillet sauté onion with 2-tablespoons olive oil for 3-4 minutes over medium heat, until translucent and thoroughly cooked. Set aside to cool down.
Combine avocado with lemon juice, remaining olive oil, grape tomatoes, sautéed onion, basil, capers, olives, salt and pepper.
Stir in pasta, mix thoroughly.
Top with hard-boiled eggs, radishes and feta cheese before serving.
