Preheat oven to 425°F and lightly grease a baking sheet.
Roast squash, flesh down, in center of oven for 30 mins (or til tender). Scoop & mash flesh when cool.
Place onion, sage, butter, salt & pepper in skillet. Cook 5 mins til onion is golden. Add garlic, cook 1 minute.
Combine onion mixture, squash and goat cheese.
Fill wonton wrapper with 1 tablespoons filling (flour surface under to prevent sticking). Wet edges and top with second wrapper. Press down around filling to seal and remove air. Place on towel to dry slightly, turning. Fill the rest of wontons the same way.
Cook butter & hazelnuts over medium heat until butter browns, about 3 minutes Remove from heat, season with salt & pepper, and keep warm.
Gently boil 5 qts salted water in 6qt pot. Cook in 3 batches, about 6 mins each (will rise to surface). Transfer to shallow pan with some cooking water to keep raviolis warm. When all cooked, plate and top with sauce. (may also steam).