Preheat the oven to 425 degrees. Arrange the chips in a single layer on a large baking sheet. Spoon the beans evenly over the chips then top with chicken, cheese and onion. Bake for 15 to 20 minutes, until the cheese is melted and bubbly. Remove from oven.
Combine lime juice and sour cream. Spoon over the nachos and top with salsa.