1) To make the guacamole: in a medium bowl, coarsely mash the avocado. Lightly mix in the onion, coriander and the lime juice. Season the guacamole liberally with salt and pepper.
2) To make the chips: preheat oven to 200°C.
3) Brush each tortilla lightly with oil. Slice the tortillas into 8ths. Using two baking sheets, distribute half the chips onto each sheet, making sure they are evenly spread out and not overlapping. (If the chips overlap they will not crisp in the oven.) Bake on the top rack until golden and crispy, about 10 to 12 minutes. Remove from the oven to a serving bowl. Season with salt and serve immediately.
Cook's Note: Season your chips with chipotle powder and/or garlic salt before baking for extra flavour.