Place shredded cheese, onion, mayonnaise and cayenne pepper in a large bowl. Stir until well combined. Place a 3-inch custard cup upside down in the middle of a 10-inch spring form pan.
Sprinkle half of the pecans in the bottom of the pan. Spread cheese mixture on top of pecans. Cover with plastic wrap and chill the mixture until firm, at least 1 hour. When ready to serve, unmold the cheese ring onto a platter and pat remaining pecans onto top and sides of ring. If desired, spoon strawberry preserves in the center. Serve with crackers.