Preheat the oven to 220°C (425°F) with a rack in the centre. Line a rimmed baking sheet with parchment.
Cut the potatoes into 2 cm (3/4 inch) cubes, toss with half the garlic-infused oil and half the salt and spread on the tray.
Roast the potatoes for 15 minutes, until starting to brown.
Trim the green beans. Pat the salmon dry with paper towel.
Stir the potatoes, push them to the sides and add the green beans and salmon. Brush the salmon and beans with the rest of the oil and the lemon juice, then season well with the black pepper and remaining salt.
Roast for 10 to 12 minutes, until the salmon flakes easily and reaches 63°C (145°F) in the thickest part.
Scatter the chopped dill over the salmon and potatoes and serve straight away.
Tips
Cut the potatoes small so they crisp in the same time.