How to Make It
Roast the jalapeño directly over a gas flame or under the broiler until charred all over. Transfer to a bowl, cover with plastic and let stand for 10 minutes. Peel, stem and seed the jalapeño and transfer to a blender. Add the feta, hot water and 1/4 cup of the olive oil and process until very smooth. Scrape into a bowl; season with salt and pepper.
Arrange the watermelon and tomatoes on a large platter, scatter the basil on top and drizzle with the remaining 1 tablespoon of olive oil. Season with salt and pepper; serve with the feta sauce.