Make the Caramelo: In a small heavy saucepan bring sugar and water to a boil, stirring until sugar is dissolved. Boil syrup, without stirring, until golden caramel. Immediately pour the some of the caramel into each tuna can, tilting them to coat the bottom and sides. Let caramel cool.

(Drizzle any remaining caramel onto a sheet of parchment or waxed paper in decorative squiggles. Let the squiggles harden and use them as a garnish for the flan.)

Make the flan: Preheat the oven to 325 degrees F.

In a large bowl, whisk together condensed milk, coconut milk, eggs, and vanilla until smooth. Divide the mixture among the tuna cans.

Place the tuna cans in a shallow baking dish and place on the middle rack in the oven. Pour in enough hot water to reach halfway up the sides of the cans. Bake the flan until just set, but still wiggly in the center, about 30 to 45 minutes. Transfer the flan to a rack and let cool. Chill the flan in the refrigerator. (The flan can be prepared up to 3 days in advance.)

When ready to serve, dip the cans in a saucepan of hot water. Using a finger, gently press down the edges of the flan, until the caramel runs up the side, which indicates that it's loosened. Invert each flan onto onto a plate. Break the caramel squiggles into pieces and insert them into the top of each flan.