In a large skillet, heat the olive oil over medium heat. Add the diced onion and sauté until translucent, about 3-4 minutes. Then, stir in the minced garlic and cook for an additional minute until fragrant.
Add the baby spinach leaves to the skillet, along with a pinch of salt and pepper. Cook until the spinach has wilted, which should take about 2-3 minutes. Stir in the crushed red pepper flakes for a hint of spice.
In a mixing bowl, combine the sautéed spinach mixture with the cottage cheese, grated Parmesan cheese, and sun-dried tomatoes. Mix well to combine all the ingredients evenly.
Preheat your oven to 375°F (190°C). Lay the flounder fillets on a clean surface, and spoon an even amount of the spinach stuffing onto each fillet. Carefully roll the fillets up, placing them seam-side down in a baking dish.
In a small bowl, mix the melted butter with lemon juice and Old Bay seasoning. Drizzle this mixture over the stuffed flounder.
Place the baking dish in the preheated oven and bake for 20-25 minutes, or until the fish is opaque and flakes easily with a fork.
