Preheat the oven to 400°F (200°C or 180°C for fan ovens).
Arrange the onion, zucchini, red peppers and chickpeas on a baking sheet/sheet pan.
Mix the oil and the Harissa together.
Toss three quarters of the oil and spice mixture with the vegetables.
Spread the vegetables evenly on the baking sheet and place in the oven for 20 minutes.
Remove the pan from the oven and toss the vegetables again with a spatula.
Nestle the salmon fillets or side of salmon amongst the vegetables.
Brush the salmon with the remaining oil and spice mixture.
Bake for 10 minutes for salmon fillets or 15 to 18 minutes for a side of salmon, until the salmon is cooked through and flakes easily with a fork.
Serve garnished with flat leaf parsley.