1. The Prep: Start by patting your fillets dry. Moisture is the enemy of a golden crust. Use a paper towel to remove all surface water, then season generously with sea salt and black pepper on both sides.
2. The Sear: Heat your olive oil over medium-high heat. You are looking for that gentle shimmer—the moment the oil starts to move like water. Carefully place your fish in the pan. Resist the urge to poke it. Let it develop that gorgeous, crusty sear for 3–4 minutes undisturbed. Gently flip and finish until it flakes easily with a fork.
3. The Aromatics: Remove the fish to a warm plate. In the same pan, drop in your butter and sliced garlic. The kitchen will fill with an earthy, toasted scent immediately. Watch the garlic closely; it should be a pale gold, not brown.
4. The Greens: Add your spinach in large handfuls. It will look like a mountain at first, but it wilts down in seconds. Toss it with the garlicky butter, a pinch of red pepper flakes, and a squeeze of fresh lemon to wake up all the flavors. Serve the fish immediately over the bed of wilted greens.

I am a firm believer that healthy eating should work around your schedule. If you want to prep this in advance, keep your components separate. You can wash and dry the spinach early in the week and store it in a container lined with a paper towel to keep it crisp. The fish, however, is best prepared fresh. If you do have leftovers, store the fish and spinach in an airtight container for no more than 24 hours. To reheat, I suggest a very quick steam or a gentle warm-up in a skillet with a teaspoon of water—do not microwave, as fish proteins will toughen rapidly.