Gently mix lemon juice with avocado; reserve. In a large frying pan, cook potatoes in hot oil, turning frequently, until tender and lightly browned, about 5 minutes. Gently fold avocado into hash browns and continue cooking until well browned, about 3 minutes. Top each serving with 1 tbsp sour cream and 1/2 tbsp salsa. Sprinkle each with 1/2 tsp cilantro.