Preheat the barbecue or broiler. Halve tomatoes, zucchinis, eggplants, and squashes lengthwise. Grill or broil vegetables until softened and lightly browned on both sides. Let cool.
Chop vegetables into small pieces, then toss them together in a large bowl. Mix in onion, turmeric, cumin, canola oil, orange juice, and salt to taste. Cover and chill in the refrigerator for about 30 minutes. Serve on top of sliced, toasted whole-wheat bread.