Peel the vegetable onion, cut off the upper third, blanch in boiling salted water for 5 minutes, remove and rinse briefly. Remove the inside of the onion and chop finely.
Mix the minced meat with the chopped onions, egg, chives and oat flakes, season with salt, pepper and thyme. Stuff the vegetable onions with the mixture. Place in a buttered ovenproof dish, top with flakes of butter and breadcrumbs.
Bake in the preheated oven at 200C ° for 45 minutes. Cover after 30 minutes if necessary.