Preheat oven to 375°F (190°C).
Lay the salmon fillet flat on a cutting board. If it's thick, you can butterfly it slightly or pound it gently with a meat mallet to even out the thickness for easier rolling.
In a small bowl, combine the ricotta, wilted spinach, lemon juice, optional zest, garlic, salt, and pepper.
Spoon and gently spread the ricotta mixture evenly over the salmon, leaving about ½ inch around the edges.
Starting from one of the shorter sides, carefully roll the salmon into a log. Use toothpicks or kitchen twine to hold it together. I used twine to hold everything together.
Lightly brush the outside of the roll with olive oil. Sprinkle with a little more salt and pepper.
Place the salmon roll seam-side down in a baking dish lined with parchment paper. Bake for 20–25 minutes, or until salmon is cooked through and flakes easily with a fork.
Let it rest for 5 minutes before removing toothpicks or twine. Slice into 1-inch rounds and serve warm.