Chop the watermelon into small, even chunks using the large knife and cutting board. Place the chunks in a mixing bowl.
Juice the lime using a citrus press or by hand, then measure out approximately 2 tablespoons of fresh lime juice.
Add the lime juice and a pinch of salt to the chopped watermelon. Toss gently to combine and evenly distribute the flavors.
Transfer the flavored watermelon mixture to a shallow dish or tray. Spread it out evenly for quick freezing.
Place the dish in the freezer. Every 30 minutes, stir the mixture vigorously with a fork to break up ice crystals and ensure an even, slushy consistency. Repeat this process 4 times, total freezing time about 2-3 hours.
Once the mixture is firm but still scoopable, serve the watermelon slush immediately in chilled glasses, garnished with a lime wedge if desired. The texture should be crystalline and slightly melted, with a crisp, icy appearance.