Preheat oven to 425F. Toss the cauliflower with 2 tbsp olive oil to lightly coat them. Add half the minced ginger, and half the minced garlic, plus a good pinch of salt and pepper. Spread the cauliflower in a single layer on a large baking sheet and roast until the tips of the cauliflower are golden brown, about 25-30 minutes. Remove and set aside.
Meanwhile about 15 minutes before the cauliflower is finished roasting, in a Dutch oven or large, heavy-bottomed pot over medium heat, warm the remaining tbsp olive oil. Add the onion and a dash of salt and cook, stirring occasionally, until the onion is turning translucent, about 3 minutes.
Add in the tomato paste and 1/3 cup of stock. Stir till smooth and well blended.
Return the soup to the pot. Taste and re-season with salt and pepper, to taste. If the soup needs more acidity, stir in 1 or so tsp of red wine vinegar or lemon juice, to taste.
If the soup is thicker than you'd like, just add in some more stock or water, a little at a time, till you are happy.
Ladle the soup into 4 bowls. Top each with ¼ of the cauliflower florets, a sprinkle of sesame seeds and fresh cilantro, as well as a dollop of yogurt if you want.
Make this soup vegan by using melted coconut oil in place of the olive oil, and vegetable stock instead of chicken stock.
This soup will keep in the fridge for a few days. You can also freeze it, for up to two months.
I say it serves four, it can probably serve five depending on appetites.