To make eggs, fill a medium saucepan half way up with water; place over medium-high heat. Bring water to a boil and add vinegar; reduce heat to a simmer. Crack eggs, one by one, into a cup and slide gently into simmering water; cook until egg whites have set, about 3 to 4 minutes. Cook 4 eggs at a time. Remove eggs to a plate with a slotted spoon; cover to keep warm.
To make polenta: slice polenta into 8 rounds. Combine chili powder and garlic powder in a cup; dust mixture over polenta rounds. Place a large nonstick skillet over medium-high heat; add oil and cook polenta until brown on both sides, about 3 minutes per side. Remove from heat and keep warm until ready to use.
To assemble, place two polenta rounds on each of 4 plates. Top each with an egg, 2 T cheese, 1/4 cup of salsa, 1 T sour cream, avocado and green onion.