Preheat oven to 425°. Season hens and hen cavities with salt and pepper.
Blend 3 tablespoons I Can't Believe It's Not Butter!® Spread, shallot and tarragon in small bowl. Evenly spread under skin, then place 1 lemon wedge in each hen.
Arrange hens breast side up in 18 x 12-inch roasting pan on rack; tie legs together with string. Roast uncovered 15 minutes.
Meanwhile, melt remaining 3 tablespoons Spread in 12-inch nonstick skillet over medium-high heat and cook onion, stirring occasionally, 2 minutes or until softened. Add mushrooms and cook, stirring occasionally, 4 minutes or until golden. Stir in bread, 3/4 cup broth and parsley. Season, if desired, with salt and ground black pepper. Spoon into greased 1-quart casserole.
Decrease heat to 350° and place stuffing casserole in oven with hens. Continue roasting hens 30 minutes or until meat thermometer inserted in thickest part of the thigh reaches 180° and stuffing is golden. Remove hens to serving platter and keep warm. Remove rack from pan.
Skim fat from pan drippings. Blend flour with remaining broth; stir into pan drippings. Place roasting pan over heat and bring to a boil over high heat, stirring frequently. Reduce heat to low and simmer, stirring occasionally, 1 minute or until gravy is thickened. Serve gravy and stuffing with hens.