Make sure your shrimp are de-veined and that the shells and tails are removed. Place them in a medium bowl.
In the shrimp bowl, squeeze the grapefruit and orange juice into the shrimp. Add the salt and cumin. Stir to combine. Let the shrimp marinate in the refrigerator for 30 minutes (up to 2 hours).
While the shrimp is marinating, peel and slice the jicama into strips approximately 1/2" thick. Place them in a medium bowl. (You can add the jicama dressing now however they will start to get soggy - I prefer to wait until I am ready to assemble).
Heat a large nonstick skillet over medium heat. Remove the shrimp from the marinade. Cook the shrimp until they just turn white or opaque, then flip and cook on the other side, approximately 2-3 minutes. If the shrimp starts to curl, it is done (or possibly over-done) so watch for the color to change and the shrimp to be firm. Remove from heat and set aside.
Add the lime juice, cilantro, and salt to the jicama. Toss to combine and season to taste.
Assemble the tacos by layering the jicama slaw on the bottom, then the shrimp. (For me this was 6 medium shrimp per taco). Top with the avocao and your favorite toppings such as radishes, sour cream, lime wedges, etc. You can even add some orange or grapefruit segments on top for some extra citrus punch!