Season the salmon fillets. Preheat oven to 350°F (177°C). Pat salmon fillets dry with a paper towel, then place on a rimmed baking sheet. Season with 1 tsp Kosher salt and ¼ tsp freshly ground black pepper. Set aside.
Make the topping. Heat 2 Tbsp olive oil in a skillet over medium heat. When hot, add shallot and cook until softened, stirring occasionally, about 3-4 minutes. Add 2 cloves chopped garlic and ¼ tsp crushed red pepper flakes, then stir. Cook 1 minute more. Add 1 (5-6oz) bag of baby spinach, ⅓ cup chopped sun dried tomatoes, 2 Tbsp thinly sliced basil, 1 tsp lemon zest, and remaining ½ tsp Kosher salt. Stir well, then continue cooking until spinach has wilted.
Finish the topping. Transfer the spinach mixture to a mixing bowl, then allow to cool slightly, about 5 minutes. Add ¾ cup ricotta cheese, then mix very well.
Assemble. Carefully divide the ricotta mixture between each piece of salmon, then pile on top, covering the entire fillet.
Bake, then serve. Transfer to the preheated oven and cook for 15 minutes, or until the internal temperature of the salmon reaches 120°F (49°C). Serve immediately with remaining 2 Tbsp julienned basil, lemon wedges, and a pinch of flaky sea salt.
