1) Preheat the oven to 400 degrees F.
2) Place beets wrapped completely in foil and roast until a knife slices through beets easily, about an hour (Beets can be cooked before hand and kept in the refrigerator until you want to use them). While beets are roasting, combine the balsamic vinegar, garlic, mustard (used to thicken, but one teaspoon of tahini sauce can be used instead if you prefer.) and olive oil in a jar or bowl with a lid and shake. Season the vinaigrette, to taste, with salt and pepper.
3) Once beets are cooked through, remove the skin by rubbing a paper towel over beets. Keeping the beets on their cooking foil, dice in 1/4" pieces. Toss the cubes in a small bowl with enough dressing to coat.
4) Combine greens, walnuts, avocado, and red onion in a large bowl (Place sliced onions onto the top of the avocados prior to tossing to help prevent avocados from browning). Add crumbled goat or feta cheese and toss the ingredients together. Toss beats and dressing to taste just prior to serving. Enjoy!