Wash the arugula thoroughly and pat it dry.

Drain the canned tuna and flake it apart with a fork.

Halve the avocado, remove the pit, scoop out the flesh, and dice into bite-sized pieces.

In a large bowl, combine arugula, flaked tuna, diced avocado, halved cherry tomatoes, and sliced red onion.

Whisk together lemon juice and olive oil in a small bowl; drizzle over the salad and toss gently to coat.

Serve immediately on plates or in a large bowl. Season with salt and pepper before serving.