Heat oil in a skillet over medium high heat. Add sausage; cook until well browned, 3 to 4 min.
In a bowl, whisk together eggs, milk and onions. Reduce heat to low; add egg mixture to skillet. Gently move a heatproof spatula across the bottom and side of the skillet until eggs are cooked but still moist.
Divide egg mixture among tortillas, placing in a row across centre of each. Top with cheese, salsa and cilantro, and serve.