Preheat oven to 400°F (200°C). Spread beetroots out on a parchment lined baking sheet and cook for 40 minutes or until tender.
Meanwhile, heat oil in a medium sized frying pan over medium-high heat. Cook garlic and beet greens until wilted, around two minutes. Set aside and allow to cool for later.
For the dressing: In a small bowl, whisk together balsamic vinegar, canola oil, honey, dry mustard, and salt.
Once the beetroots are cooked to fork-tender and cooled for 20 minutes, mix them in a medium-sized bowl along with the cooked beet greens and feta cheese.
Layer salad in four Mason jars, each one as follows: ½ cup spinach, ¼ cup quinoa, ½ cup beet mixture, ½ cup spinach, ¼ cup quinoa, ½ cup beet mixture. Top with 1 tbsp (15 mL) of balsamic vinegar dressing and 2 tsp (10 mL) walnuts.