Add the salmon, spinach, cheese, lemon juice, and pepper to the bowl of a food processor fitted with the blade attachment. Blend until evenly ground and combined.
1 lb boneless, skinless salmon, 1 packed cup baby spinach, 2 oz feta cheese, 1 1/2 tbsp lemon juice, dash ground black pepper
Form the mixture into 4 equal patties and lay on a parchment paper lined baking sheet. Cover and chill for 1 hour.
Add the avocado to a small bowl and mash. Add the remaining sauce ingredients to the bowl and mix together until evenly combined. Set aside.
1/2 ripe avocado, 4 tbsp sour cream, 4 tsp lemon juice, 1 tsp minced garlic
Grill the burgers for roughly three minutes per side, just until cooked through.
Toast the buns, add a salmon burger to each, top with a bit of sauce and onion, before finishing off with the top bun.
4 brioche buns, thinly sliced red onion
Serve warm & enjoy!