Preheat your oven to 350°F/180°F. Line a deep baking dish with parchment paper.
Slice the beetroot into medium-sized cubes, and place in the lined baking dish. Pour olive oil over and bake for 25-30 minutes.
Remove from oven and allow to cool for a few minutes.
Place the cooked beets in a food processor or blender. Pulse only a few times.
Add all the other burger ingredients in a large bowl and add the beets. Combine thoroughly. If the mix starts to become too mushy or liquidy, add more breadcrumbs.
Once the mix is ready, start shaping it into burger patties one by one. When each one is done, transfer the patty onto a newly lined baking tray.
Bake the patties for 30 minutes. Flip them at 15 minutes to allow even cooking across the entire burger.
Prepare the dressing by combining the ingredients in a large bowl. Try to mash the avocado as best as possible until you’ve achieved your desired consistency.
When cooked, remove the beet patties from the oven. Allow to cool for a few minutes.
Assemble the burgers by placing the patties in the buns, and top with the avocado mix and red onion.
Serve immediately and enjoy!