Roast the vegetables. Preheat the oven to 400°F. Coat a baking dish with olive oil and add the acorn squash, tomatoes, onion, and garlic. Drizzle with more olive oil and season with salt and pepper. Roast for about 40 minutes, until the squash is fork-tender.
Soak the cashews. While the vegetables roast, cover the cashews with boiling water and let them soak.
Cool. Remove the vegetables from the oven and let them cool for about 10 minutes. Squeeze the soft garlic cloves out of their skins and discard the skins.
Blend. Add the roasted vegetables, drained cashews, basil, vegetable broth, coconut milk, coconut sugar, and additional salt and pepper to a large blender. Start on low and gradually increase to high. Blend 1 to 2 minutes until completely smooth.
Adjust. If the soup is too thick, add more broth 1/4 cup at a time. It will thicken more in the fridge.
Serve. Divide into bowls and top with a drizzle of coconut milk, salt, and pepper.