Drain the lychees and jackfruit well. Reserve 1/2 cup (120 ml) of syrup from the lychees. Dice the pineapple, mango, and avocado into small, spoonable pieces. If using nata de coco and grass jelly, drain and cut them into bite-size pieces as needed.
In a small pitcher or measuring jug, whisk together the chilled coconut milk, sweetened condensed milk, reserved lychee syrup, cold water, and salt until smooth. Taste the mixture; it should be sweet and creamy, with enough liquid to sip through the melting ice.
Divide the pineapple, mango, lychees, jackfruit, avocado, nata de coco, and optional grass jelly among four tall glasses or bowls.
Pile crushed ice over the fruit in each glass. Stir the coconut milk mixture once more, then divide it evenly over the ice.
Garnish with toasted coconut if desired. Serve immediately with a long spoon and a wide straw so everyone can enjoy both the fruit and the sweet icy liquid.