Escarole is a broad-leaved endive (as opposed to curly endive or frisée) and is most often utilized in Italian cooking. It is less bitter than the other vegetables in the endive family and is most similar in taste to radicchio and chard. In terms of cooking, escarole is very much like spinach, in that it shrinks down to almost nothing when cooked for a long time. So the secret is to buy a little more more than you think you need.
To prepare the braising liquid for the haddock, I simply cook the onions, garlic, tomatoes, portobello mushrooms and escarole in some marinara sauce. You don't really need much of the sauce as the escarole exudes water when cooked. Add salt and pepper to taste. This process should take just about 5 minutes.
Now prepare the haddock fillet by seasoning it with salt and pepper. Also, remove the skin if you haven't done so. Place the fish in a shallow oven pan and add the braising liquid together with its vegetable contents. Heat your oven to 450F and start cooking. Depending on how big of a fillet your haddock is, the dish should be cooked in around 20-30 minutes.
Haddock is a wonderful fish for this braising method of cooking. It is able to absorb the braising medium and take on the flavor of the escarole. Serve the fish together with the vegetables and some of the braising liquid. It should make for a pretty delicious meal. Best of all, it is so simple and should take less than 40 minutes to prep and cook. What a time saver!