Place large skillet over medium heat. Sauté onion and sweet potato in olive oil. Remove sausage from casings and place into pan, breaking it up as it cooks. Once sausage is thoroughly cooked, stir in zucchini, corn and spices. Cook another 3-4 minutes. Add in the quinoa to warm it through. Spoon into lettuce leaves, top with cilantro and red onion if desired and serve.