Using a large knife, cut small watermelon in half. Slice off the ends and discard them. Chop watermelon into triangular slices, about an inch thick.
Prep your outdoor grill or indoor griddle and set for high heat.
Use tongs to place four slices of watermelon in the center of the grill.
After 2 minutes, use tongs to lift the slices by the rind to see if the grill marks are set underneath. If not, cook for another minute.
Once the grill marks develop, use the tongs to carefully flip the slices over.
Grill for another 2-3 minutes.
Remove the four watermelon slices and place on a plate or a cutting board to cool.
Repeat with all the slices, grilling four at a time.
Arrange watermelon slices on a platter and top with lime juice (from ½ of a lime) and the Tajin seasoning.
Cut the remaining 1 ½ limes into slices to use as garnish.
Notes
If you need to substitute Tajin seasoning, you can use the same amount of red, mild chile powder.
You can also make this recipe using a large watermelon (about 20 lbs). You will end up with about 50 slices, which can be seasoned with the juice of one lime and 5 teaspoons of Tajin seasoning.
Thicker slices of watermelon do best on the grill. Each of the pieces should have about an inch of rind.