Step 1
Mix 2¼ tsp. freshly ground pepper, 2¼ tsp. ground Sichuan peppercorns, 1½ tsp. sugar, and 1½ tsp. Diamond Crystal or 1 tsp. Morton kosher salt in a small bowl to combine; set spice mixture aside.
Step 2
Toss 1 lb. medium shrimp, peeled, deveined, tails left on, and ⅓ cup cornstarch in a large bowl until shrimp are evenly coated. Set aside.
Step 3
Heat ⅓ cup vegetable oil in a large nonstick skillet over medium-high. Working in batches and adding more oil as needed if pan looks dry, cook one 16–18-oz. tube precooked polenta, cut into 1″ cubes, in a single layer, turning halfway through, until golden and crisp, 10–14 minutes per batch. (Be patient; the polenta takes a long time to crisp up. Don’t fuss with it too much.) Transfer polenta to a large bowl.
Step 4
Working in batches and adding more oil as needed if pan looks dry, cook reserved shrimp in a single layer in same pan, turning halfway through, until golden brown and crisp, about 2 minutes per batch. Transfer to bowl with polenta.
Step 5
Add 5 Fresno chiles, thinly sliced, to same pan and cook, stirring often, just until tender, about 1 minute. Transfer to bowl with polenta and shrimp.
Step 6
Add 1 bunch scallions, cut into 2″ pieces, white pieces halved if thick, to same pan and cook, stirring often, just until tender, about 1 minute. Transfer to bowl with polenta, shrimp, and chiles and sprinkle reserved spice mixture over. Toss until combined and everything is evenly coated. Taste and season with more salt if needed.