*Cook's Note: Depending on your heat preference, you may remove the seeds from the jalapenos or leave them intact.
1) Set 1 of the oven racks on the lowest shelf and preheat oven to 180C/Gas 4.
2) Line a baking tray with greaseproof paper. Make 8 (5-cm) balls out of aluminium foil. Spray 3 wire cooling racks with non-stick cooking spray and place one of the aluminum balls in each of the corners of two of the racks.
3) Lay 1/3 of the crisps on one of the racks. Top each crisp with a jalapeno slice and sprinkle with 1/3 of the red onions, and 1/3 of both the Cheddar and Oaxaca cheeses. Repeat with the remaining crisps and the other 2 racks.
4) Stack the racks on top of one another and set into the greaseproof paper-lined baking tray. Bake in the oven on the bottom rack for 7 minutes or until the cheese begins to bubble.
5) Sprinkle with fresh oregano. Serve immediately with the salsa, sour cream, and guacamole.