Heat the oil in a sauté pan and gently cook the onions and garlic until soft. Add the red peppers, 2/3 cup/150 ml of the stock, and the tomato paste. Season with salt and pepper, and simmer until the vegetables are tender and the liquid has completely evaporated. Purée with an immersion blender and transfer to a metal or glass bowl.
Stir the gelatin into the remaining stock in a small saucepan, and heat, stirring to dissolve. Mix it well into the purée. Set the mixture on a bed of ice and cool until the mixture mounds when dropped from a spoon. Check the seasonings, adding lemon for acidity if needed. (The mixture should be highly seasoned because the cream, once added, will dilute the taste a bit.)
Whip the cream and gently fold it in. Pour the mixture into a mold, cover, and chill until serving, at least 4 hours. This is very good with the cauliflower salad on the side for crunch.