Place each salmon fillet on a flat surface. Season both sides with salt, pepper, 1 tablespoon olive oil and lemon juice. Cut a slit or pocket about 3/4 quarter of the way through, being careful not to cut all the way.
Squeeze excess liquid out of the spinach discard liquid. In a medium-sized bowl, mix together the spinach, cream cheese, parmesan cheese and garlic. Season with salt and pepper.
Fill salmon ‘pockets’ with 1-2 tablespoons of the spinach dip, spreading evenly with the back of the spoon.
For Stove Top:
Heat butter and remaining oil in a skillet (or non stick pan) over medium-high heat. Add the salmon and fry until golden (about 6 to 7 minutes). Carefully flip and allow to cook on the other side until golden and cooked through (another 6-7 minutes, depending on the size of your fillets).
Optional: cover with a lid and continue cooking for a further 2-3 minutes, if necessary, until cooked through.
Transfer to a warm plate to make garlic butter.
Garlic Butter: Melt the butter in the remaining oil/juices in the pan leftover from the salmon. Add the garlic and lemon juice; saute until garlic is fragrant (about 30 seconds). Remove and serve with the salmon.
For Oven Baked Salmon:
Preheat oven to 350°F (175°C). Place stuffed salmon fillets in a shallow lightly greased baking pan. Bake for 10-15 minutes or until salmon is cooked through, opaque in centre and flakes easily with fork.
Pour pan juices out into a skillet or frying pan. Add butter, garlic and lemon juice; saute until garlic is fragrant (about 30 seconds). Remove and serve with the salmon.