In a medium-sized bowl, mix the lime (or lemon) juice, olive oil, and salt. Whisk it well, until it is thoroughly emulsified. Add the chopped dill, and mix again.
ADD THE REST AND MIX
Slice the radishes thinly. If they are very large, cut them in half, and cut into thin half-circles. Add them to the bowl with the dressing. Chop the avocados into bite-sized chunks, and add them also to the bowl. If the cooked shrimp are very large, cut them in half; otherwise, just add them to the bowl with everything else.
Mix the salad thoroughly, so that all ingredients are glazed with the dressing. Serve immediately.
Notes
I tend to use frozen cooked shrimp. Thaw them under running cold water for about 20 minutes, drain (dry) them, then proceed with the recipe.