Lay sardines side by side on a clean, dry kitchen towel (or on paper towels) and gently roll together into a cylinder to remove excess moisture. Refrigerate until ready to use. When ready to use, season with salt and pepper and toss in flour to coat completely. Remove and shake off excess flour. (Alternately, sprinkle both sides of sardines with flour.)
To a nonstick skillet over medium-high heat, add sardines. Cook, undisturbed, until the skin is crispy and lightly charred, 2 to 3 minutes per side. Turn sardines over and cook for another 2 to 3 minutes. Add garlic, lemon juice, oregano, and red pepper and continue to cook until heated through, another 3 minutes.
Season sardines a final time with sea salt and black pepper and arrange on a serving platter. Spoon lemon-olive oil mixture over fish. Garnish with lemon slices. Serve immediately.