1. Cut fish into 3-inch strips. Sprinkle evenly with 1 tsp. Greek seasoning, 1 tsp. salt, and 1/2 tsp. pepper.
2. Combine flour, cornmeal, baking powder, remaining 1 tsp. Greek seasoning, 1/2 tsp. salt, and 1/2 tsp. pepper; stir well. Add 2 cups cold beer and egg, stirring until thoroughly blended and smooth.
3. Pour oil to a depth of 2 to 3 inches into a Dutch oven; heat to 375°.
4. Dip fish strips into batter, coating both sides well; shake off excess. Fry fish, in batches, 2 minutes on each side or until golden (do not crowd pan). Drain on paper towels.
5. Spread top half of each bun evenly with tartar sauce. Place 1 lettuce leaf and 1 tomato slice on bottom half of each bun; top each with 2 fried fish strips and top halves of buns.