Simmer watermelon, chia seeds, stevia, and lemon juice in a large sauce pan until the fruit breaks down and slightly thickens. About 15 mins.
Strain watermelon mixture through a fine mesh sieve over a large bowl, and stir to help separate the juice from the pulp. You should get about 2 cups worth of juice.
While the juice is still warm add to a food processor with vinegar, peppercorns, herbs, salt, and Xantham Gum and blend until smooth.
Stir in the fresh herbs, transfer to a bottle of your choosing, and refrigerate.