HEAT oven to 450ºF. Place squash, parsnips, onions, peppers and garlic in 15x10x3/4-inch baking pan. Add 2 Tbsp. dressing; toss to coat. Spread to evenly cover bottom of pan.
BAKE 40 to 45 min. or until vegetables are tender and golden brown, stirring occasionally. Spoon into large serving bowl. Add spinach; toss lightly.
TOP with bacon and nuts. Drizzle with remaining dressing.