Bring a medium pot filled halfway with water to a boil. Once boiling, add in the shrimp and cook for 2 minutes or until shrimp are opaque and cooked through. Drain shrimp into a colander and add about 1 cup of ice on top and set in the refrigerator.Meanwhile, spiralize the cucumbers with Blade A and then trim them and pat dry thoroughly.In a medium mixing bowl, add in the ingredients for the dressing. Whisk together and set aside.In a large mixing bowl, add in the cucumbers, cilantro, pepper, grapefruit slices and toss together. Add in the shrimp, dressing and mix well to incorporate. Season the ceviche with some salt. Portion into plates and garnish with avocado.