Preheat oven to 350°F (175°C).
Mix quinoa, leek, olive oil, harissa, salt, pepper, and herbs in a bowl.
Stuff beets with quinoa mixture, leaving a little space for swelling.
Place beets snugly in a baking dish; add broth and lemon juice around beets to keep moist.
Cover with foil and bake 30 minutes, spoon reserved liquid over stuffing, then bake 15-20 minutes until quinoa is tender and beets are soft.
Serve warm or room temperature with yogurt or tahini.