In a small bowl or jug mix olive oil, Greek Grilling Spice, lemon juice and salt together to create a marinade.
In a large baking tray, layer the potatoes to cover the bottom of the tray. Drizzle half the marinade over the potatoes and coat well to ensure all potatoes are covered.
Place in oven and cook potatoes for 15 minutes.
After 15 minutes, remove the tray from oven, add fish fillets on top of the potatoes and scatter asparagus and broccolini around the edges. Drizzle the rest of the marinade over the fillets, asparagus and broccolini and add the lemon slices spaced around the tray.
Place tray back in the oven and bake for a further 15 minutes or until the fish has cooked through.