Preheat oven to 400F. Trim greens and ends off of beets. Wrap in tin foil and roast in oven for 50 minutes. While beets are roasting, prepare quinoa and lentils per package instructions. Saute diced onions in olive oil for 5 minutes. Add in garlic for 30 seconds, cooking until slightly browned and aromatic. Set aside.
When beets are finished cooking, let cool to a heat at which you're able to handle them. Using a box grater, shred beats to a shredded cheese consistency. This should yield ~2 cups. Wrap beets in paper towel, or place in fine colander, and press excess juice out. Beet juice can be reserved and used in smoothies or other recipes.
Using a food processor, pulse rolled oats into a flour-like consistency. Mix all ingredients together, stirring with wooden spoon to combine. Divide beet mixture into six patties, pressing them firmly together. Heat 1 tsp oil in cast iron pan, then add beet burgers to pan, cooking three minutes on each side. The burgers are done when outside is browned and crispy.*
To speed up the cooking process, prepare beets, lentils, and quinoa the night before. I recommend preparing quinoa and lentils in bulk and freezing extra so that they're readily available for quick meals.Beet burgers are also delicious when baked in the oven instead of on the stove. The oven yields a crispier burger and allows for more hands free time. Bake the patties at 400F for 30 minutes, turning halfway through.