Toss the shrimp with a pinch of sea salt, the garlic powder, onion powder, oregano and red pepper flakes. Set aside.
Heat up 3 tbsp of olive oil in a large skillet and sauté the onion until translucent. Add the bell pepper and cook together until they start to get a little bit of color around the edges. Stir in the garlic and scallions, toss to coat and add the shrimp. Quickly toss everything together on medium flame for about 1 minute and set aside to cool. Sprinkle with the parsley. ( Make sure not to overcook the shrimp as it will continue to cook when we crisp up the polenta cakes.)
In a large bowl mix together the cold polenta with the egg yolk until smooth. Fold in the shrimp mixture and shape it into 12 patties. Set on a platter and refrigerate for about an hour until set.
Heat up a seasoned cast iron skillet on a medium flame. Add a lug of olive oil, just enough to coat the bottom nicely, we are not frying anything, we just want the polenta cakes not to stick.
Working in batches crisp up your shrimp cakes until golden brown on both sides, about 3 minutes per side. Using a spatula transfer them to a platter and serve drenched with theChimichurri sauceon top.