Preheat oven to 425 degrees F. In a large 9×13 casserole dish (line with foil for easy clean up if you want), add the tomatoes, onions, garlic, and olive oil. Mix together to combine everything (I used my hands) and generously sprinkle salt, pepper, and the dried thyme all over. Bake in the oven for 35-45 minutes until tomatoes begin to char and release their juices. Let it cool for 5-10 minutes.
Add the roasted tomatoes, onions, and garlic to a high speed blender. Add the sugar, fresh basil, another 1/2-3/4 tsp of sea salt, 1/4 tsp black pepper, and coconut milk. Blend on high until nice, smooth, and creamy.
Transfer soup into a medium pot and heat over medium heat. Stir in the pesto. Taste the soup and add more salt and pepper if needed. Add more coconut milk if you want it thinner. Serve with crusty bread, paninis, grilled cheese, or whatever you’d like! Enjoy!