Wash and remove the kale stems, and then tear the leaves into 3-inch pieces. Place the kale in a stand mixer with the olive oil and turn the mixer on a medium speed setting. Agitate the kale in the mixer until it is glossy and torn into 1-inch pieces.
Peel the onion and shave it into thin rings using a mandolin (the Japanese style are the easiest to use) about 1/16-inch thick. Bring the vinegar and water to a simmer and add the salt, cumin, chile flakes, and thyme. Pour the vinegar mixture over the sliced onions and set in the fridge for a couple hours, up to overnight.
In a blender combine the cucumber, vinegar, mustard, salt, shallots, and garlic, and blend until smooth. Once smooth, slowly drizzle the oil into the blender cup until completely emulsified.
In a dry blender combine the salt, chili powder, citric acid, and cayenne until slightly powdery.
In a large mixing bowl toss the kale, watermelon, cucumber, and radish with 1/2 cup of the vinaigrette, season the salad with salt as you toss. Transfer to a bowl and garnish with ¼ cup of the pickled red onion and the crumbled cheese, and finish the salad with a couple dashes of the sour salt.