Allow beets to cool. Under running cool water, peel beets. Then cut beets into small ½-inch cubes.

Meanwhile, rinse wild rice in a colander under running water for about 1 minute. Add rice, 1¼ cups (296 milliliters) water and butter to a small saucepan. Bring to a boil. Cover with a lid and reduce heat to low. Simmer and cook 45 minutes. Remove from heat and allow to rest an additional 10 minutes. Fluff with a fork and set aside.

To make salad, combine beets, rice, cabbage, walnuts and lemon juice in a bowl. In a small bowl, combine garlic, mustard, vinegar, salt and remaining olive oil. Whisk to combine. Pour over salad and stir to combine well. Serve at room temperature or cold.