Preheat the oven to 450 degrees F. Line a baking sheet with foil and lightly coat with cooking spray.
Place the tomatoes in a single layer on the prepared baking sheet.
Drizzle the tomatoes with the olive oil, and sprinkle them with garlic, oregano, salt and pepper.
Roast until the tomatoes are slightly shriveled and soft, 15 to 20 minutes. Roughly chop the tomatoes and set aside.
In a small bowl, whisk together the lemon juice, olive oil, agave (or honey) and salt.
The spaghetti squash:
Using a large, sharp knife, pierce a spaghetti squash in several places.
Place the spaghetti squash in a glass baking dish and cook in the microwave on high for about 15 minutes, turning the squash halfway through cooking.
Before handling, let the squash stand for 10 minutes. Cut it in half lengthwise and scrape out the seeds and fibers. Using a fork, twist out strands of the spaghetti squash flesh and place in a large bowl. Let stand at room temperature.
Add the roasted tomatoes, mozzarella, basil and dressing to spaghetti squash. Toss gently to combine. Serve.