Blanch the tomatoes and peel them. Cut the flesh into pieces removing the tough cores and place in a bowl. Clean the watermelon flesh of seeds and add to the tomatoes.
Add blanched almonds, peeled garlic and shallot, vinegar, oil, season with salt and freshly ground black pepper and blend everything in a blender.
Strain through a sieve into a clean bowl (glass or ceramic) and refrigerate for at least an hour to chill.