In a saucepan, add 1 cup of rinsed quinoa and 2 cups of water. Add garlic powder and ground cumin to the cooking water. Bring to boil, then reduce heat to simmer and cook for about 15 minutes or until quinoa is tender and water has mostly absorbed.
While quinoa cooks, sauté red onions in a pan with 1 teaspoon olive oil (optional) over medium heat until translucent, about 5 minutes. Set aside.
In a mixing bowl, combine cooked and cooled quinoa with rinsed black beans, sweet corn, cherry tomatoes, sautéed onions, and diced bell peppers. Mix well.
In a small bowl, whisk together lime juice, avocado oil, and optional additional cumin and garlic powder for the dressing. Pour over the quinoa salad and stir to coat evenly.
Garnish with chopped cilantro if using and adjust salt to taste. Serve chilled or at room temperature, with optional avocado slices on top.