Mince the garlic. Rinse and drain the quinoa thoroughly.
In a medium saucepan over medium heat, warm 2 tsp toasted sesame oil. Add the minced garlic and the rinsed quinoa and toast, stirring frequently, for 3–4 minutes until the quinoa is fragrant and lightly golden.
Carefully add 1 3/4 cups vegetable broth, increase heat to high and bring to a boil. Reduce heat to low, cover, and simmer for 15–20 minutes until the quinoa is tender and liquid is absorbed. Remove from heat and let sit covered for a few minutes, then fluff with a fork.
While the quinoa cooks, slice or halve the mushrooms and slice the green onions.
Heat a large skillet over medium. For an oil-free method, use a splash of vegetable broth or water; otherwise add a little sesame oil. Sauté the shiitake mushrooms for 5–6 minutes until softened, then remove them from the pan.
Sauté the portobello mushrooms, then the cremini mushrooms in the same pan, adjusting time as needed so each variety is cooked through. (You may cook all together if preferred.)
Return all cooked mushrooms to the large pan. Add the cooked quinoa, sliced green onions, 2–3 Tbsp sesame seeds, and 1 Tbsp tamari. Stir and sauté together for 1–2 minutes to combine and heat through.
Taste and add more tamari if desired. Serve sprinkled with additional sesame seeds if you like.