Preheat the oven to 400 degrees F. Coat the eggplant, zucchini, squash, onion, and garlic with the nonstick cooking spray.
Mix the cayenne pepper, seasoning salt, and chili powder in a bowl. Season the vegetables with 1/4 of the cayenne pepper mixture. Toss to mix then add another 1/4 of seasonings and toss to mix. Repeat this step until all of the seasoning has been added.
Coat a baking pan with the nonstick cooking spray. Place the vegetables in the pan and cook in the oven for approximately 35 minutes, or until browned, stir often.
Put the vegetables in a blender and blend until they reached the desired consistency. Sprinkle the salt and pepper over the mixture and serve.