Use the chef's knife and cutting board to dice the ripe watermelon into 1-inch cubes, set aside in a mixing bowl.
Thinly slice the red onion into rings or strips, then add to the bowl with watermelon cubes.
Remove seeds and thinly slice the jalapeño peppers, then add to the bowl. Adjust the amount based on desired spiciness.
Use a lime squeezer or your hand to extract fresh lime juice from the lime, then pour over the mixture in the bowl.
Add a pinch of salt to enhance the flavors, then gently toss all the ingredients together until evenly combined and coated with lime juice.
Transfer the salad to a serving plate or bowl, and serve immediately to enjoy the fresh, juicy textures and vibrant flavors.