1Rinse shrimp; pat dry. Line a 4-cup bowl with enough plastic wrap so that it hangs over edge of bowl. Arrange a layer of shrimp in a spiral pattern in bottom of bowl. Add additional layers, filling all spaces and pressing down, until bowl is full.
2Fold the plastic wrap over shrimp. Place two 1-pound cans on top of shrimp and refrigerate 1 hour.
3Meanwhile, in small bowl combine cocktail sauce, lime juice and chile powder; mix well. Cover and refrigerate until serving.
4Unwrap bowl. Pull plastic wrap away from top of bowl. To unmold, place a large platter upside down over bowl, then turn platter and bowl over; remove plastic wrap. Garnish the shrimp spiral with watercress and lemon slices. Serve with sauce.