Kotopoulo me Riganatos is oregano chicken: grilled chicken carried by a heavy oregano seasoning. The defining move is the herb load, rigani being Greek oregano, used here in a quantity that makes it the lead flavor rather than a background note. This sits apart from the lemon-led and plainly grilled chicken preparations in the Greek set because the oregano is the whole identity of the dish, not an accent.
The make is an oregano-forward seasoning, a grill, and a finish. The chicken is rubbed or marinated with a generous amount of dried Greek oregano, with olive oil, garlic, and salt, and usually some lemon, the oil helping the dried herb adhere and carry. It is grilled over direct heat until charred and just cooked, then frequently finished with another scatter of oregano off the heat so the herb stays aromatic rather than fully cooked out. Good execution shows oregano you can smell before you taste, distributed evenly so every bite carries it, on chicken that still has grill char and a juicy interior. Sloppy work shows in two ways: dried oregano applied dry and bare so it scorches into bitter black flecks over the fire, or so timid a hand that the dish is just plain grilled chicken with no real herb presence, which defeats the entire point. The usual chicken failure applies on top, a breast left on the heat until it is dry and stringy turns aggressive oregano into something harsh and dusty. The balance to hit is bold piney oregano and char against moist chicken, with the herb fragrant rather than burnt.
Variation tracks how the oregano is handled and what it is served with. Adding the bulk of the herb at the finish keeps it fresh and resinous; building it into a longer marinade gives a deeper, more cooked-in herb flavor with less top-note. Lemon often rides alongside to cut the resinous edge, and a yogurt or tzatziki accompaniment is common to soften and round the herb, though the dish itself is defined by the chicken and the oregano. A tzatziki-and-meze service builds around this kind of plate and deserves its own article rather than being crowded in here, as do the lemon and skewered chicken forms.