Preheat oven to 350 degrees F. In large mixing bowl, combine squash, zucchini, eggplant, onion, and garlic. Toss vegetables with oil, salt, and pepper. Place mixture on a baking pan and roast until the vegetables are soft, about 30 minutes. Cool the vegetables to room temperature. Once cooled, chop into 1/2-inch dice. Over medium-high heat, melt butter in a large nonstick skillet. Add pecans, stirring frequently to coat with butter and until golden brown, about 3 minutes. Add chopped vegetables to pan and cook for about 1 minute. Season with salt and pepper.