First, cook the shrimp. Heat the olive oil in a large skillet over medium high heat and add the lemon zest to really infuse into the oil. Then add the shrimp and cook it until it is pink and opaque, for about 5 minutes. While it cooks, flavor it with the salt, garlic powder, dried onion and cumin. Once it is cooked through, set it aside to cool. While it cools, make the amazing lemon mayo. Wrap a bowl with a cold, damp towel. Whisk the lemon juice, Dijon and egg yolk together in that bowl until it is bubbly and thoroughly mixed. Then keep whisking (it's an arm workout) while you slowly pour in the olive oil until you have a gorgeous, thick mayo. 

Combine the mayo, celery, cashews, dried tarragon, dried thyme and ground mustard in a bowl. Take the cooled shrimp and roughly chop it into little pieces and stir it in thoroughly with the rest of the salad. Seal it up and let it chill for at least 3 hours, or up to overnight. About 40 minutes before you are ready to serve, pre-heat the oven to 375. Line a sheet tray with a silicone mat. Place the sweet potato thin round slices in a single layer on the sheet tray. Then stir the olive oil, cumin, garlic powder, salt and black pepper together in a bowl and brush it generously on each sweet potato round. Bake them for 25 minutes or so until tender and slightly crisp. Let them cool for a few minutes, then scoop a spoonful of salad on each round. Serve immediately! Keep any leftover shrimp salad for sandwiches or wraps.