Wash the Hokkaido, halve it, scrape out the seeds, and cut into large pieces.
Peel the onions and cut into wedges.
Put both in a baking dish along with rinsed and chopped thyme.
Toss with olive oil and vinegar, sprinkle with salt and pepper, and bake in a preheated oven at 200 degrees Celsius (392 degrees Fahrenheit) for about 30 minutes.
Cut the bread into slices, place slices of Brie on them, put them on the dish in the oven, and bake until golden, about 7-8 minutes.
Serve immediately with a little pasta, optionally tossed with diced tomatoes.