Thinly slice the garlic and red onion, chop the sun-dried tomatoes, drain the tuna and beans, and zest and juice the lemon. Flake the tuna into large chunks with a fork — keep them chunky, not shredded. Line everything up; this moves fast once the heat is on.

Pour the olive oil into the large skillet over medium-low heat. Add the garlic, sun-dried tomatoes, capers, oregano, and red pepper flakes. Cook, stirring often, until the garlic is pale gold and fragrant, 2–3 minutes. Keep the heat gentle — browned garlic tastes bitter, and this oil is the dressing.

Add the cannellini beans and red onion to the skillet. Toss to coat in the garlicky oil and cook, stirring occasionally, until the beans are heated through, about 3–4 minutes. Taste and season with salt and pepper — remember the capers, olives, and feta all bring salt, so season lightly.

Remove the skillet from the heat. Add the lemon zest and juice, then the flaked tuna and olives. Fold gently — just enough to warm the tuna through and coat everything in the oil. The tuna is already cooked, so this is about warming, not cooking.

Add the arugula and fold until just wilted, about 1 minute. The residual heat softens the leaves without turning them to mush. Taste once more and adjust lemon or salt.

Crumble the feta over the top, drizzle with a little extra olive oil, and serve warm with crusty bread for scooping up the garlicky oil at the bottom of the bowl.