Bring 1 1/2 cups of slightly salted water to a boil. Add the rice and cook covered on medium heat for 30-40 minutes, until rice absorbs the water and is tender. When cooked, transfer the rice to a plate and allow to cool.
Meanwhile sauté the onion in a skillet with oil, set over medium heat. Allow it to get translucent. Add garlic, cumin, thyme and paprika. Cook for 30-60 seconds, just until fragrant. Remove from heat.
Grate the beet on a box grater. Squeeze out most of the liquid with a cheesecloth, then transfer it to a large mixing bowl.
Add the onions, beans, rice, mustard, coriander, oats and egg. Mix with a spatula or your hand thoroughly, until the mixture is even and everything is well incorporated.
Add the breadcrumbs. You want the mixture to be pretty easy to form, but not dry or sandy. Cover the bowl with plastic wrap and chill in the refrigerator for 30 minutes or overnight.
To shape the burger mixture into patties take handfuls of the mixture and make thick disks with your hands. You need 6 pretty big patties. Keep in the refrigerator until you're ready to cook them.