Simmer milk and 1 1/2 cups water. Whisk in grits, reduce heat, and cook until thick (about 7 minutes). Stir in cheese, 2 Tbsp. butter, and 1 tsp. Cajun seasoning. Season with salt.

Spread grits into an 11x8-inch dish. Refrigerate until cold (about 30 minutes).

Pat shrimp dry. Toss with salt and 1 1/2 tsp. Cajun seasoning.

Melt remaining 2 Tbsp. butter in a large skillet. Cook celery and bell pepper until soft (3-4 minutes). Add white scallion parts, garlic, and tomato paste; cook 2 minutes more.

Push veggies to the side. Add shrimp to the center; cook until opaque (3-4 minutes). Remove shrimp mixture to a plate.

Use a 2-inch round cutter to cut 15 rounds from chilled grits. Cut each round in half horizontally to get 30 thin disks.

Set up three bowls: flour mixed with remaining 1 tsp. Cajun seasoning, beaten eggs, and panko. Coat each disk in flour, then egg (shake off excess), then panko (press to stick). Freeze for 10 minutes.

Heat oil in the skillet. Fry disks in batches until golden and crisp (1-2 minutes per side). Drain on paper towels; sprinkle with a pinch of salt.

Arrange on a platter. Top each with a shrimp and some vegetable mixture. Sprinkle with green scallion parts. Serve warm.