Preheat oven to 375 degrees F. Mix all ingredients except tortillas. Warm tortillas until pliable (about 10 second in microwave). Wet one side of tortilla and place wet side down. Spoon on filling ingredients. Roll to hold in filling. Spray baking dish with non-stick coating. Lay chimichangas seam side down on baking dish. Bake 25 minutes. Serve with cheese sauce. For Cheese Sauce: In a small saucepan melt butter or margarine. Stir in flour, salt, and pepper. Add milk all at once. Cook and stir over medium heat until thickened and bubbly. Cook and stir 1 to 2 minutes more. Remove from heat. Add cheese, stir until melted. Just before serving, add lemon juice and stir until smooth.