Heat a skillet to medium high heat and add in the olive oil. Sear each piece of salmon for a few minutes (skin side up). Remove from the pan and set aside.
Drain any excess oil and add in a little of the butter. Add in the garlic and sauté for about 20 seconds, then add in the wine.
Add the rest of the butter, lemon juice, zest, half of the parsley and capers. Add the salmon back into the pan, skin side down and cover. Continue cooking the salmon for a few more minutes.
Remove from the pan and along with some of the sauce, leaving some in the pan. Add in the fresh spinach and toss in the sauce. Sauté for about 2 minutes, or until cooked through. Serve with the salmon, garnish with parsley.