Heat your grill to a medium-high setting.
In a food processor, pulse the salmon fillets until coarsely minced, then transfer to a large bowl.
Stir in the panko breadcrumbs, Greek yogurt, whole grain mustard, lemon juice, onion powder, sea salt, black pepper, and cilantro until thoroughly blended.
Shape the mixture into four equal patties.
Lightly grease the grill grates with oil.
Grill the salmon patties for about 4-5 minutes on each side, ensuring they reach an internal temperature of 145°F.
While the patties are cooking, prepare the avocado topping by combining cubed avocado, chopped tomato, diced red bell pepper, and lime juice in a separate bowl.
Gently fold the ingredients together to create a fresh salsa.
Toast the multigrain buns on the grill for 1-2 minutes until lightly browned.
To assemble, place a grilled salmon patty on each bun, add fresh spinach, and top with the avocado mixture.
Enjoy your delicious creation!