In a large skillet, cook sausage and onion until sausage is cooked through; drain well.
Stir in 1/4 teaspoons garlic powder and 1/8 teaspoons pepper; set aside.
For filling, combine cottage cheese, cream cheese, 1/2 cup of the Montery jack cheese, 1/4 teaspoons garlic powder, and 1/8 teaspoons pepper; set aside.
Grease a 2-quart rectangular baking dish; set aside.
Place noodles on a clean surface. Spread cheese filling evenly over noodles. Sprinkle sausage mixture and mushrooms on top. Roll up each noodle into a spiral. Place lasagna rolls, seam sides down, in a prepared dish; set aside.
For sauce, in a small saucepan, melt butter. Stir in flour, tarragon, and 1/8 teaspoons pepper. Add milk. Cook and stir until slightly thickened and bubbly. Cook and stir 2 minutes more. Remove from heat. Stir in 1/2 cup of the cheese. Pour sauce over the pasta spirals.
Cover and bake in a 350 degree oven for 25 minutes. Remove cover; sprinkle with the remaining cheese, and bake 15 more minutes.