Preheat oven to 375 degrees. Line a sheet pan with parchment paper.
In a medium sized bowl, whisk together the first 8 ingredients. Then slowly add the olive oil, whisking all the while until fully incorporated.
Pour half of the vinaigrette into an airtight container and place the in the fridge to use for future salads.
Place the salmon pieces on the prepared sheet pan, season with ¼ tsp salt and ¼ tsp pepper, and place the remaining ingredients (onions, peppers, olives, capers, feta and tomatoes) evenly throughout the sheet pan.
Pour the remaining half of the marinade over the salmon and veggies.
Bake for 15 minutes, or until cooked to your liking.
Optional- Broil for 2-3 minutes for a crispy top.