Combine plum tomatoes, refried beans, cilantro, lime juice, hot Mexican chili powder, minced garlic, and minced red onion in a medium bowl.
Scrape the mixture onto a 12- to 14-in. round serving plate and smooth into a 10-in. circle with a spatula.
Spoon guacamole over cheese layer and spread into an even layer.
Drain salsa in a strainer to get rid of excess juice. Spread salsa in an even layer over bean the bean layer.
Arrange chopped tomatoes on top of salsa and top with cheese.
Spider Web Garnish:
Place sour cream in a ziptop bag; seal bag and snip a small tip off one corner.
Pipe a spiderweb design over guacamole and onto the plate.
Decorate with a plastic spider or cut one black olive in half and place cut side down in the center of the sour cream web for the body of the spider. Cut a second black olive into legs and arrange around the body of the spider.