Peel the jicama, then cut it, the pear, and the jalapeno in thin slices. A mandolin is helpful here.

Cut the skin and pith from the grapefruit and supreme out the segments with a knife.

Put the fruit and jalapeno in a bowl, squeeze the juice of the lime over it, and season with a little bit of salt, and a small drizzle of olive oil, if you want. Mix together and set aside. 

Finely slice the onion (thinnest setting on the mandolin). Pat dry with paper towels.

Heat up a bit of vegetable oil in a small pan.

Toss the sliced onion in flour, so that it leaves a thin coat.

When the il is hot, deep fry the onion in small batches until dark golden brown. When a batch is ready, remove it from the oil with a slotted spoon and place it on paper towels. Sprinkle some salt on the finished batch and leave it to drain. 

Coarsely chop the cilantro leaves (reserve the stems for something else, like pesto) and mix them with the fruit in the bowl. Taste and adjust seasoning if necessary. 

Drain excess marinade and arrange salad on serving platter or individual plates. Garnish with a generous amount of fried onion.

Serve immediately (with avocado slices if you wish).