Pat the fish dry and sprinkle with salt and pepper. In a large oven-safe saute pan, heat the olive oil over medium heat and cook the onions and fennel until tender and golden, 8 to 10 minutes. Add the tomatoes and herbes de Provence and cook until the tomatoes begin to soften, another 5 minutes. Increase the heat to high and deglaze the pan with the wine, chicken stock and lemon juice and let bubble for 1 minute.
Nestle the fish fillets into the pan, sprinkle with salt and pepper and top each with a pat of butter. Place into the oven and cook until the fish is cooked through, 8 to 10 minutes.
Broil just until a bit crusty, about 1 more minute. Squeeze lemon juice on the fish and serve.