Preheat oven to 400°F.
Using a mandolin or a sharp knife, slice the red onion and shallots as thin as you can. Place the sliced red onion into a jar or a glass container. In a small pot, combine apple cider vinegar, distilled vinegar, maple syrup and a generous pinch of salt. Add about ⅓ cup of water and bring to a boil. Once boiling, pour the brine over the sliced red onions. Cover and set aside to cool.
Peel and devein the shrimp. Remove the skin from the salmon and cube into 1 inch pieces.
In a large bowl, combine cubed salmon, cleaned shrimp, minced garlic and parsley (reserve about 1 tsp for serving). Season with salt and pepper generously and splash with olive oil. Mix well, until the seafood is coated in seasoning. Transfer the seasoned shrimp and salmon onto a sheet pan in a single layer. Roast until cooked through, about 15 minutes.
While the seafood cooks, heat a generous splash of olive oil over medium heat in a frying pan. When it starts to smoke, add the shallots. Fry, stirring occasionally, until golden brown and crispy, about 8-10 minutes. Transfer onto a paper towel and let rest.
Serve the seafood medley on a bed of greens of your choice (we use watercress). Garnish with pickled onions and crispy shallots. Sprinkle with remaining parsley and enjoy!
