Prepare pasta according to package directions. Meanwhile, coat a large skillet with olive oil over medium-high heat until hot. Add diced chicken and sauté for 4 minutes or until cooked through; drain and set aside.
Recoat the skillet with olive oil over medium-high heat until hot. Add mushrooms, carrots and green onions; sauté for about 6 minutes; set aside. Place flour in a medium saucepan. Gradually add milk, whisking until well blended; stir in sherry (if using). Bring mixture to a boil over medium heat and cook for 5 minutes or until thickened, stirring constantly. Stir in salt, cayenne pepper and green peas. Reserve one cup of sauce and set aside.
In a medium bowl, combine Ricotta cheese, 1 cup of Mozzarella cheese and the Swiss cheese. Preheat oven to 400 degrees. Spread 1 cup of the sauce on the bottom of a 9- x 13-inch baking dish or pan. Arrange 4 lasagna noodles (3 lengthwise, 1 widthwise) over the sauce. Top with half of the cheese mixture, half of the chicken mixture and half of the remaining sauce mixture. Repeat layers, ending with 4 lasagna noodles.
Spread reserved 1 cup of sauce over the last complete layer of noodles, being sure to cover the lasagna completely. Tent it with foil and bake for 30 minutes (longer, if you made it the night before and you start out cold).
Uncover lasagna, sprinkle remaining 1/2 cup of Mozzarella cheese on top and bake, uncovered, for 5 minutes. Let lasagna stand for 5 minutes before serving.