Poaching fish is a great, easy way to cook the protein while ensuring that it retains all its moisture. And poaching something in olive oil takes that to the next level. You'll want to use a tasty extra-virgin olive oil for this because the fish will absorb a lot of the oil's flavor during the cooking process. I went with simple flavors (lemon, garlic, chile, oregano) to let the olive oil and fish shine, but it would be easy to sub in any additional herbs and spices (think rosemary or other citrus) you like.
Add the olive oil and garlic to a pot just wide enough to hold the fish fillets in a single layer without touching. Line a plate with paper towels and set aside.
Peel 1 of the lemons into strips with a vegetable peeler (to get just the yellow part of the peel). Add to the pot together with the chile flakes and oregano. Season the fish fillets with salt and pepper, to taste.
Using a deep-frying thermometer to monitor the temperature, bring the oil to 175 degrees over medium-low heat. Then, reduce the heat and adjust to maintain a steady temperature. Add the fish. (The oil temperature will drop slightly once fish is added, so slowly adjust the flame to get oil back up to 175 degrees, then reduce the heat again to maintain.) Cook until the fish is opaque, about 10-15 minutes depending on the thickness of the fillet and desired doneness.
Remove the fish and place on the paper towels to drain some of the excess oil. Cut the second lemon into slices and scatter over the fish. Serve immediately.