Halve squash lengthwise and scoop out the seeds. Place cut-side down in a microwave-safe dish and add water. Microwave on High until the flesh can be easily scraped with a fork, about 15 minutes.
Meanwhile, heat oil in a skillet over medium heat. Cook and stir onion in oil until tender. Add garlic; cook and stir until fragrant, 2 to 3 minutes. Stir in tomatoes and cook until tomatoes are warmed through.
Use a large spoon to scoop the stringy pulp from the squash and place in a medium bowl.
Toss with cooked onion-tomato mixture, feta cheese, olives, and basil.
Serve warm.
As a variation, roast tomoatoes:
Pre-heat oven to 400°F , toss tomatoes with oil, salt and pepper in a large bowl. Transfer to the prepared baking sheet. Roast until soft and wrinkled, 10 to 12 minutes. Remove from the oven. Add in a cup of cannellini (white) beans and stir to combine.
