SEASON cod filets with 1/2 tsp kosher salt and 1/4 tsp black pepper. Heat 2 tbsp olive oil in a large skillet over medium-high heat.
ADD seasoned cod filets to skillet and cook for 4 minutes. Flip and cook for an additional 3 minutes. Set aside on a plate. Filets will finish cooking later.
POUR remaining 1 tbsp olive oil into the skillet. Once heated, add diced onion and cook for 5 to 7 minutes, until it becomes translucent. Add minced garlic and reduce heat to medium. Cook for 1 to 2 minutes.
ADD in chopped sun-dried tomatoes and stir—season with remaining 1/2 tsp kosher salt and 1/4 tsp red pepper flakes.
WORK in batches to add chopped spinach and cook until spinach is wilted, for about 5 minutes total. Pour in canned coconut milk and stir to combine. Increase heat and bring to a simmer. Once simmering, reduce heat to low.
PLACE cod filets back into the skillet and cover the skillet. Let simmer until fish reaches an internal temperature of 145 °F. This will take about 4 to 6 minutes.
SERVE each filet with several scoops of the Tuscan-style veggie mixture and enjoy!