In a medium sauté pan, heat olive oil with smashed garlic clove, allowing garlic to infuse the oil, until clove just starts to brown.
Add cubed chayote squash, sauté and cook until tender, about 5 - 7 minutes. Add minced garlic and onion slices, and season with salt and pepper. Sauté until onion is translucent and chayote squash begins to brown. Sprinkle with rosemary and cook 3 - 4 minutes longer. Serve.