Heat 2 tablespoons olive oil in a large skillet over medium heat. Add the garlic and red pepper flakes; cook 1–2 minutes, stirring often, until the garlic is pale gold and fragrant. Don't let it brown darkly.

Add the cherry tomatoes, cut-side down where you can, and cook undisturbed 2 minutes, then stir and cook 1 more minute until softened and a few are lightly blistered.

Stir in the cannellini beans, broth, rosemary, salt, and pepper. Bring to a lively simmer and cook 4–5 minutes, until the liquid thickens slightly and the beans are warmed through. Gently crush a few beans with the spoon to make it creamy.

Add the drained tuna in large chunks, stirring very gently so it stays in flakes rather than shredding. Simmer 1–2 minutes, until heated through.

Stir in the spinach a handful at a time until just wilted, about 1 minute. Off the heat, stir in the lemon zest, lemon juice, Parmesan, and the remaining tablespoon of olive oil. Taste and adjust salt and pepper.

Spoon into warm bowls or straight onto plates. Top with extra Parmesan, a rosemary sprig, lemon wedges, and a pinch more red pepper flakes. Serve with plenty of crusty bread for the garlicky broth.