Preheat the oven to 400°F.
In a blender or food processor fitted with the blade attachment, blend the peppers and tomato with the olive oil, vinegar, garlic, paprika, salt and sugar.
Pour the sauce into a medium to large, oven-proof skillet (cast iron is perfect), and place it over medium-high heat.
Add the spinach and cook until it's completely wilted, about 2 minutes. Remove the pan from the heat.
Season both sides of the fillets with sea salt and freshly ground black pepper. Then add them to the pan, being sure to coat both sides with the sauce.
Place the pan in the preheated 400°F oven and cook just until the fillets are cooked through -- it should still be translucent in the center, 7 to 10 minutes.