Open the canned tuna and drain the water completely using a fine-mesh sieve or the lid of the can.
In a medium mixing bowl, combine the drained tuna, Greek yogurt, lemon juice, olive oil, dried oregano, sea salt, and black pepper.
Use a fork to flake the tuna and stir the mixture until the ingredients are well combined and the tuna is coated in a creamy dressing.
Prepare the vegetables by dicing the cucumber, halving the cherry tomatoes, and finely mincing the red onion.
Place the baby arugula in a large serving bowl to create a fresh leafy base.
Scoop the prepared tuna salad onto the center of the arugula.
Arrange the diced cucumber, cherry tomatoes, red onion, and whole kalamata olives around the tuna.
Crumble the feta cheese over the entire bowl and serve immediately for a fresh, high-protein meal.