Line two cookie sheets with aluminum foil or parchment paper.
In a small bowl, combine oil, Italian seasoning, salt, pepper and red pepper flakes and stir to combine
On the first prepared cookie sheet, place the carrots, cauliflower and peppers, not mixing the vegetables, but keeping them separated.
On the other cookie sheet, place the pumpkin, zucchini and tomatoes, also keeping them separated.
Give the oil mixture a stir and pour a little on each group of vegetables.
With your hands, gently massage the oil onto the vegetables.
Put the vegetables in the oven and set a timer for 10 minutes.
Check the vegetables at the 10 minute timer and then every 5 minutes thereafter. You want the vegetables to be soft, but not mushy, so if one vegetable gets done ahead of time, transfer it to a bowl and put the tray back in the oven.
Making the stock
While the vegetables are roasting, heat one tablespoon olive oil in a stock pot over medium heat.
When the oil is hot add the onions.
Saute the onions, stirring often until they are golden brown
Add stock and bring to a simmer.
Season broth with salt and pepper to taste.
Serving the soup
When ready to serve the soup, add the vegetables to the stock pot.
Serve each bowl with a spoonful of lemon balm pesto and a crusty piece of toasted bread.