Pound chicken breasts to ¾ inch (2cm) even thickness between plastic wrap, then pat completely dry with paper towels.
Combine oregano, garlic powder, onion powder, basil, salt, pepper, and red pepper flakes in a small bowl. Season both sides of chicken, then lightly dust with flour, shaking off excess.
Heat 2 tablespoons olive oil in a large skillet over medium-high heat. Sear chicken 4-5 minutes per side until golden and internal temperature reaches 160-163°F (71-73°C). Transfer to a plate and tent with foil.
Reduce heat to medium, add remaining 1 tablespoon olive oil to the skillet. Cook onion 3-4 minutes until softened, then add garlic and cook 60 seconds until fragrant.
Pour in white wine, scraping up browned bits from the pan bottom. Simmer 2-3 minutes until reduced by half.
Add chicken broth, cherry tomatoes, and sun-dried tomatoes. Bring to a gentle simmer and cook 4-5 minutes until tomatoes soften.
Add fresh spinach and stir 1-2 minutes until completely wilted.
Nestle chicken back into skillet, drizzle with lemon juice, and simmer 2-3 minutes to heat through. Top with Parmesan and fresh basil, then serve immediately with pasta, rice, or crusty bread.