Pat the salmon fillet dry with paper towels and season both sides evenly with sea salt, black pepper, and dried oregano.
Heat the ghee in a medium non-stick skillet over medium-high heat until shimmering.
Place the salmon skin-side up in the pan and sear for 4 to 5 minutes until a golden crust forms, then flip and cook for another 3 to 4 minutes.
Remove the salmon from the pan and set aside on a plate.
In the same pan, reduce heat to medium and add the minced garlic, sautéing for 1 minute until fragrant but not browned.
Pour in the heavy cream and squeeze the juice from the half lemon into the pan, stirring to combine with the garlic and pan drippings.
Add the baby spinach to the skillet and toss gently for 1 to 2 minutes until just wilted.
Return the salmon to the skillet, spooning the creamy garlic sauce over the top before serving immediately.