Heat the oven to 450°. In a food processor or blender, puree the bananas, curry powder, coriander, dry mustard, butter, lime zest, lime juice, salt, pepper, and 1/4 cup of the water.
Make a few deep cuts in each chicken breast and put the breasts in a roasting pan. Pour the curry sauce over the chicken, making sure the sauce gets into the cuts. Roast in the bottom third of the oven until the chicken is just done, about 20 minutes.
Remove the roasting pan from the oven and remove the chicken breasts from the pan. There should be plenty of thick sauce in the bottom of the pan. Set the pan over moderate heat and whisk in the remaining 1/2 cup water. Continue to whisk until the sauce is heated through, adding more water if you want a thinner sauce. Serve the chicken breasts with the sauce over them. Sprinkle with parsley if you like.