Pierce squash with a fork in several places then wrap it in a large piece of heavy-duty foil.
Grill the squash over medium coals on a covered grill for 45 minutes to 1 hour or until the squash can be easily depressed with the back of a long-handled spoon and turn the squash every 15 minutes a quarter turn.
Once the squash is done grilling remove it from the grill and let it stand for 10 to 15 minutes still in the foil.
Take the zucchini slices and spray both sides with cooking spray while the squash is grilling, then grill the zucchini slices on an uncovered grill for about 4 minutes or until they are tender over medium coals, turning the zucchini slices once while grilling.
Take the spaghetti squash, remove from the foil, cut in half, scooping out the seeds, and comb strands of pulp from each of the squash halves with two forks and place the strands in a large salad bowl.
Take tomatoes, beans, zucchini, and basil and add it to the squash strands and combine mixture in a small bowl with olive oil, vinegar, garlic, and salt mixing thoroughly.
Add vegetables to the mixture in the small bowl and toss them gently so that they are evenly coated.