These beet chips are a labor of love. They take a while to make and require many batches, so be prepared. They are a delicious, healthy snack for your family. My girls love them and so do I! I also found these work best in a convection oven, they cook faster and crisper...so if you've got one go for it, it will be a better chip.
Rinse and scrub the outsides of the beets. Carefully slice the beets into 1/16-inch-thick rounds using a mandolin slicer. Place in a large bowl and drizzle the olive oil over, turning to coat evenly. Lay out a single layer of beet slices on 2 baking sheets and sprinkle with freshly cracked pepper (don't add the salt at this point, as it will make the chips less crisp).
Bake for 30 to 45 minutes for a regular oven, rotating the sheets from top to bottom halfway through. Bake for 12 to 15 minutes for a convection oven, rotating halfway through. The beets will be darkened around the edges and be mostly crisp; they will firm up a little bit more once cooled. Let the chips cool, and then transfer to a bowl. Repeat with the remaining beet slices. When they are all cooked, toss with salt to taste.
For the guacamole: Mash the avocados with a fork or potato masher in a large bowl until slightly chunky. Stir in the cilantro, lime juice, tomatoes and onions. Season the guacamole with salt and pepper and garnish with olive oil.