Put the carrots and beetroot in a colander over a bowl. Add 1 tsp salt and toss to combine. Let sit for approximately 30 minutes (or longer) to release liquid until the vegetables look soft. Squeeze the vegetables to release more liquid and pat dry with paper towels to remove any excess. The less moisture in the veggies, the less soggy your burgers will be!
Heat the oil in a frying pan and sauté the onion for 3-4 minutes, until starting to soften. Remove from the heat and transfer to the bowl with the carrot and beetroot.
Place the beans and oats in a food processor and process until nearly smooth.
Add the bean mixture to the beetroot and season.
Add the beaten egg, bit by bit, mixing well as you go, until you have a sticky consistency.
Line a baking sheet with baking paper. Shape the mixture into four burgers. Bake for 15-18 minutes.
Serve on half the rocket leaves and sliced tomato.
Notes
LEFTOVER TIP: keep uncooked burgers in an air-tight container in the fridge for up to 3 days.