Watermelon cubes: Cut the ends off of the watermelon. Remove the rind from the melon by standing the watermelon up on one of the flat cut ends, then running a knife down the length of the melon just deep enough to cut off all of the green/white rind part. Continue cutting the rind off the melon until all you are left with is the meat of the fruit. From this point, trim the edges to create a large, straight-edged rectangle. Dice 2/3 cup of watermelon in to cm or smaller uniform cubes using the excess pieces from trimming the rectangle. Set the diced aside in a mixing bowl, reserved for the salad. From the large rectangle cut out either all 2-3 inch cubes or varying sizes of rectangles and cubes to use for your watermelon cups. Once you have achieved this, using a paring knife and a melon baller or small spoon cut/scoop out the middle of each rectangle leaving about 1 cm wall of melon on the edges and the bottom. Repeat this process until all the watermelon cups have been hollowed out. Place all of the watermelon cups on a plate/tray, loosely cover with plastic wrap, and refrigerate until ready to be filled.
Salad: In the mixing bowl with the reserved diced watermelon, add the diced jicama, peaches, sweet onion, garlic, jalapeno, cilantro, and lime juice. Toss gently to combine and thoroughly coat all of the ingredients with the lime juice to prevent them from oxidizing and turning brown. Season to taste with kosher salt and freshly cracked black pepper. Set aside.
Cream sauce: To a bowl add the cream fraiche, chopped cilantro, lime juice, jalapeno, and feta. Stir to combine thoroughly. Season to taste with kosher salt and freshly cracked black pepper.
Liberally fill each of the watermelon cups with the fruit salad. Garnish with a little dollop of cream sauce and a small cilantro leaf. Serve immediately.