Cheese Patties: Cut each cheese piece into 3 rounds for a total of 12 slices. Set aside.
Combine 17-3/4 oz. water, 2-1/4 oz. cornstarch, 2 oz. flour, 4-1/4 oz. crackers, baking powder and salt in blender container. Blend until smooth. Pour into bowl; let stand 30 min. to hydrate. Combine remaining cornstarch and flour in second bowl. Process 12-3/4 oz. crackers to fine crumbs; place in third bowl. Whisk eggs and remaining water in fourth bowl. Place remaining crushed crackers in fifth bowl.
Coat each cheese slice in 5 steps: First, dredge in cornstarch-flour mixture; then dip in blended cracker mixture; then coat in fine cracker crumbs; then dip in egg-water mixture; finally, coat in the remaining crushed crackers.
Fry Cheese Patties in 350°F deep fryer 1 min. or until crust is set. Refrigerate until ready to use.
For each serving: Heat 1 fried Cheese Patty in 350°F standard oven 4 to 6 min. or until heated through. Place cheese patty on bottom half of bun. Top with 1 grilled beef patty, 2 Tbsp. lettuce, 1 tomato slice, 2 pickle chips, 1 red onion slice and 2 tsp. mayonnaise. Cover with top of bun.