Place tomatoes and onion in a bowl; drizzle with 3 Tbsp seasoning, oil, vinegar, salt, and pepper. Toss to mix; spread out on Bake & Roll.
Bake until tomatoes are soft, juicy, and starting to burst, about 30 min.
Scrape mixture into a Multipurpose Pot - 12 C ; add broth. Bring to a boil; reduce heat and simmer for 10 min to let flavours blend. Working in batches, purée in a blender until smooth. Return soup to pot; stir in remaining 2 Tbsp (30 ml) dip mix. Reheat over medium-high, stirring often, until warm. If making ahead, refrigerate up to 3 days or portion and freeze up to 3 months.
To serve, stir yogurt with aioli mix and milk. Spoon soup into bowls and top with a swirl of yogurt mixture. Top with finishing sauce, if desired.