In a blender or food processor blend the basil, mint, garlic and lemon juice.
With the blender or food processor running, slowly drizzle in the olive oil until fully incorporated.
Pour the mixture through a fine sieve pressing on the solids, then discard the solids.
Stir the salt and pepper into the the dressing. Then taste and adjust seasonings.
Arrange the cubes of watermelon, tomatoes and Feta cheese on 6 plates.
Drizzle with the dressing.