Roasting: Into a baking tray, add the halved tomatoes, quartered onions, quartered bell peppers, garlic cloves, olive oil, thyme leaves, salt and black pepper. Give everything a good mix together. Pop in the oven and bake for 30 minutes. Once baked, allow the veggies to cool for 10 minutes.
Blending: Add the cooled roasted veggies, oat milk, vegan basil pesto, dried basil, onion powder, garlic powder, chili flakes. Make sure you scrape all that veggie-infused olive oil from the baking pan into the blender too! Blend together until smooth.
Final touches: Pour the thick soup into a pot. Add the water into the blender, and give it a swirl to get all that soup goodness. Pour into the pot with the soup. Heat over medium-high heat, and once it starts to boil, simmer for 10-15 minutes. Serve with fresh basil and vegan grilled cheese sandwiches!