Preheat oven to 200C/180C fan forced. Cook the pasta in a large saucepan of salted boiling water following packet directions or until al dente. Drain.
Heat oil in a large frying pan over medium-high heat. Add broccolini, zucchini and beans. Cook, stirring, for 4-5 minutes, adding 125ml (½ cup) water halfway through cooking to steam.
Place the flour, mustard powder and 125ml (½ cup) of in a medium saucepan. Stir until mixture forms a smooth paste. Whisk in the remaining milk. Place saucepan over medium-high heat. Cook, whisking, for 2-3 minutes until sauce is thick. Whisk in the olive oil spread, nutritional yeast flakes, if using, and half the parmesan. Season. Transfer to a large bowl. Add the pasta and two-thirds of the vegetable mixture.
Lightly grease a 4L (16 cup) ovenproof dish with olive oil. Arrange salmon fillets in the dish. Spoon over mornay mixture and scatter over remaining vegetable mixture. Sprinkle with remaining parmesan and bake for 25-30 minutes or until golden and bubbling around the edges. Set aside for 5 minutes to cool slightly before serving.