In a medium saucepan combine quinoa, cumin, ¼ teaspoon salt, and 1½ cups water. Bring to a boil, then reduce heat to low, cover, and simmer gently until tender and water is absorbed, about 15 minutes. Let stand off heat for 5 minutes, then fluff with a fork.
Prepare a hot grill fire, preheat a gas grill on high heat for 10 minutes, or heat an indoor grill or grill pan on high heat (for a grill pan, lightly brush with vegetable oil).
Rub steak all over with ¾ teaspoon salt and chili powder. Place on grill or in grill pan and cook, turning once, until browned and cooked to desired degree of doneness, 2-3 minutes per side.
Transfer steak to a cutting board and let rest 5 minutes.
While steak rests, in a medium bowl stir together avocado, corn, beans, tomatoes, onion, cilantro, lime juice, and remaining ½ teaspoon salt.
To serve, divide quinoa among 4 bowls. Thinly slice steak across the grain and place on top of quinoa along with avocado-corn salsa.