Combine the vinegar, oil, salt, pepper, herbes de Provence, and lemon juice in a bowl, whisking until emulsified.
Pour over the chicken, taking care to completely coat it. Insert the reserved squeezed lemons, plus the rosemary and garlic into the cavity. Layer the onions in a roasting pan and place the chicken on top. Slice the fennel in half lengthwise and surround the chicken with it, cut side down.
Put the chicken in the oven and immediately reduce the temperature to 250 degrees F and roast for 1 1/2 to 2 hours, basting occasionally.
This chicken gets very dark when roasting. If you're concerned about burning, tent with foil, however be sure to remove it for the last 15 minutes of cooking.
This recipe was created by a contestant during a cooking competition. It has not been tested for home use.