For the truffle creamed spinach: In a medium skillet over medium heat, heat the oil. When shimmering, add the onions and saute until translucent, 3 to 4 minutes. Remove excess liquid from the defrosted spinach by placing it in a colander or squeezing it in a dish towel. Finely chop the spinach, then add it to the skillet with the onions and cook for approximately 3 to 4 minutes. Add the truffle peelings, cream cheese, and heavy cream. Bring to a simmer and cook until liquid is reduced, approximately 10 minutes, stirring occasionally so nothing sticks to the bottom of the pan. Season to taste with salt and pepper. Set aside.
For the oysters: Preheat the oven to 350 degrees F. In a Dutch oven fitted with a deep-fry thermometer, heat the oil to 375 degrees F.
Place the shucked oysters on paper towels to dry. Place the oyster shells on a sheet pan and fill the shells with the creamed spinach mixture. Place the shells in the oven for approximately 10 minutes or until the spinach is slightly toasted on top.
Place the flour in a bowl and season with a big pinch of salt and a few grinds of pepper. Dredge the oysters in the flour. Fry the oysters until golden brown, about 3 to 5 minutes depending on their size. Place on paper towels to drain. Season with salt while still warm.
Take the spinach-stuffed oyster shells out of the oven, place a fried oyster on top of each shell and serve.