1.Cook pasta in large saucepan of boiling water, uncovered, until just tender; drain. Rinse under cold water; drain, then pat completely dry with absorbent paper.
2.Place two sheets of pasta on board; layer half of the salmon evenly onto sheets. Top each layer of salmon with another sheet of pasta, avocado, another sheet of pasta and the remaining salmon. Top each of the stacks with a sheet of pasta.
3.Cut each stack in half; halve each piece diagonally. Place two pieces of the stacks on serving plates.
4.Place juice, oil, dill and mustard in small jug; whisk until dressing is blended. Place spinach in medium bowl, pour half of the dressing over leaves; toss gently to combine.
5.Drizzle lasagne stacks with remaining dressing; serve with spinach.