Grate the beets roughly into a bowl. Be prepared, this may be a bit messy! You may want to wear some gloves.
Combine the beets with peanut butter, oats, flour, rosemary, thyme, garlic and onion powder and salt. Take care that the peanut butter is spread throughout the mixture, and not just one lump. Use your hands to properly knead everything into a well mixed mass.
Dividing the mixture in four equally sized portions and roll 4 balls. Squeeze these balls flat into patties. Make sure they are not too thick. Place them in the fridge for 10 minutes.
In the meantime, prepare your toppings and sauce. Cut the avocado in thin slices, and the red onion in halve rings. Place aside.
Prepare the sauce by mixing the mustard, ketchup and sugar syrup.
Heat the olive oil in a pan on medium heat. Bake the beet burgers about 8 minutes per side on medium heat.
Serve the burgers on a bun, with avocado, pineapple, rocket, onion and burger sauce.