If the cuttlefish aren't cleaned, pull the head and tentacles away from each body, then remove the hard cuttlebone and the innards. Cut the tentacles off just below the eyes and press out the hard beak at the center. Rinse everything and pat dry, keeping the fins and skin on the bodies.
Heat the oven to 180 C / 350 F (160 C fan). Finely chop the tentacles. Warm 1 tbsp oil in a 28 cm / 11-inch oven-safe skillet over medium heat and cook the tentacles with the 2 minced garlic cloves for 3 minutes, until opaque and fragrant. Scrape into a mixing bowl and wipe the skillet clean.
Add the breadcrumbs, Parmigiano, egg, 3 tbsp parsley, capers, lemon zest, 1/4 tsp salt and the pepper to the tentacles. Mix until the filling holds when pressed in your palm. Spoon it into the bodies until each is only two-thirds full, without packing it down, and close each opening with a toothpick.
Return the skillet to medium heat with 3 tbsp oil. Cook the onion and sliced garlic for 5 minutes, until soft and pale gold. Pour in the wine and simmer for 2 minutes, then add the tomatoes, 1/4 tsp salt and chili flakes. Simmer for 5 minutes, until the sauce loses its raw edge.
Nestle the stuffed cuttlefish into the sauce in a single layer and spoon some sauce over the tops. Cover tightly with the lid or foil and bake for 30 minutes. Remove the cover and bake for 15 minutes more, until a paring knife slides into the thickest part of a body with no resistance and the sauce coats the back of a spoon.
Rest the cuttlefish in the skillet for 5 minutes. Pull out the toothpicks, slice each body into rounds about 2 cm thick and spoon the sauce over. Scatter with the remaining 1 tbsp parsley and serve with lemon wedges.