Heat the oven to 325. Line a baking sheet with aluminum foil and spray it with cooking spray. Lay the bread cubes in a single layer and mist with cooking spray. Bake for 15 minutes.*
Combine* the toasted bread cubes, the tomatoes, the corn and the avocado in a mixing bowl and lightly toss together.
*While the bread cubes are baking, place the chopped bacon in a medium skillet and bring over medium heat. Cook, stirring occasionally, until bacon pieces are crispy. Remove the bacon with a slotted spoon to a stack of paper towels to drain. Transfer a tablespoon of the bacon grease from the pan into a bowl to make the dressing. Add the rice vinegar, mustard, canola oil, water, pepper, salt and onion powder to the bacon grease in the bowl and whisk together until well combined.
Add the bacon pieces to the salad mixture from step two and stir together. Toss the salad in the dressing before serving. Each serving makes about 1 1/3 cups of salad tossed in about a tablespoon of dressing.
If you will not be serving the entire salad at once, store the unused bread cubes in a Ziploc bag, the rest of the salad mixture tossed together in the refrigerator, and the dressing stored separately in the refrigerator. You will want to heat the dressing leftovers before using again because the bacon grease will cause it to thicken when cool.