Preheat the oven to 400F and line a baking sheet with parchment paper. Spray with olive oil cooking spray.
Place quartered potatoes on the baking sheet, drizzle with olive oil and toss. Spread evenly over the baking sheet and roast for 15 minutes.
Brush salmon filets with olive oil, sprinkle with dill and salt and pepper. Set aside.
Make the Greek Salsa: in a medium size bowl combine ¼ cup olive oil, garlic, lemon zest and juice, oregano, feta, tomatoes, cucumbers and kalamata olives. Season with salt and pepper. Stir gently to combine.
When potatoes have cooked for 15 minutes, carefully take out of the oven and push to the sides, place sliced red onion in the center of the sheet, and place salmon on top. Scatter lemon slices around the sheet. Place back in the oven and continue to cook for about 10-12 minutes until salmon is cooked and potatoes are tender.
To serve: Place salmon and potatoes on a plate, spoon salsa over salmon. Enjoy!