In a shallow bowl, combine soy sauce, rice vinegar, maple syrup, garlic, and sriracha. Add the tempeh and turn over to coat completely. Marinate 15-30 minutes, turning once.
Meanwhile, place quinoa and vegetable stock in a small pot and bring to a boil. Reduce the heat to low, cover with a tight fitting lid, and let cook for 15 minutes or until all the water is absorbed. Turn off the heat and let rest, covered, for 5-10 minutes.
In a large skillet, melt the coconut oil over medium heat. Add the marinated tempeh in a single layer, shaking off any excess marinade. Cook 7-8 minutes, turning once, until the tempeh is golden brown.
While the tempeh is cooking, combine 2 teaspoons cornstarch with 1 tablespoon water in a small bowl. Add to the marinade and mix thoroughly.
When the tempeh is done cooking, remove it to a plate. Add the marinade to the pan and stir until thick, about 1 minute. Return the tempeh to the pan and stir to coat. Remove from the heat.
In a large bowl, add a scoop or two of quinoa, then layer in tempeh, carrots, green onions, and radishes. Sprinkle to taste with sesame seeds and hemp hearts.