Cut the avocado in half, remove the pit, and scoop out 4 round pieces. Drizzle with lemon juice.

Mix olive oil, lemon juice, and salt and pepper in a bowl to make the olive dressing.

Skewer cherry tomatoes, avocado pieces, and mozzarella cheese onto picks. Arrange on a plate and drizzle evenly with olive dressing.

Finely chop the onion and soak in water for 5 minutes. Drain and squeeze out excess water. Mash the remaining avocado in a bowl with a fork.