Cook the quinoa. Add ½ cup quinoa and 1 cup of water to a saucepan and bring to a boil. Cover, decrease the heat to low, and cook 15-20 minutes until all the water is absorbed. Remove from heat and let steam, covered, for 5 minutes.
Meanwhile, prep the corn. If using frozen corn, thaw and move on to Step 4. If using canned corn, drain and rinse and move on to Step 4.
If using corn on the cob, boil a large pot of water. Once boiling, add the corn and cook for 3 minutes until the starchiness is just gone. Drain and immerse it in ice water to stop the cooking and to set the color. When the corn is cool, cut the kernels off the cob, cutting close to the cob.
Add the corn, onion, cilantro, cherry tomatoes, quinoa, and 3 oz crumbled feta to a large bowl.
Make the dressing. In a small bowl, mix together the mayonnaise, lime juice, chili powder, cumin, garlic, liquid sweetener, and salt.
Add the dressing to the large bowl with the other ingredients and stir so that everything is coated in the dressing. Add more salt to taste.
Divide the corn salad between four bowls. Garnish with more cilantro and another ounce of crumbled feta cheese.