Whisk together the lime juice, soy sauce, and sesame oil in a shallow dish; add the tempeh cubes to the dish and toss to coat. Set aside.
Heat a non-stick skillet to medium-high, then add the avocado oil. Add the cubed sweet potato. Cook, turning the sweet potatoes often, until golden brown and tender, 5-10 minutes. Transfer the sweet potatoes to a medium bowl, along with the quinoa, and keep warm.
To the same skillet, add the tempeh cubes and any liquid from the marinade that wasn't absorbed. Cook the tempeh on all sides until golden brown and crispy. Add the quinoa and sweet potatoes back to the skillet and fold in the cashews. Remove from heat.
In a small bowl, whisk together the tahini, miso, and water until smooth. Add vinegar to taste. Set aside.
To serve, arrange the baby spinach on two plates and divide the quinoa mixture onto the spinach. Drizzle with the Tahini-Miso Sauce and Sriracha.