Heat oven to 400 degrees F. Cut baguette into 1-inch pieces. Spread onto a baking sheet and spritz with nonstick cooking spray. Bake at 400 degrees F for 10 minutes, until lightly toasted. Remove from oven and let cool.
In small bowl, whisk together white wine vinegar, Dijon or spicy brown mustard, sugar, salt and pepper. While whisking, add olive oil in a thin stream.
In large bowl, toss together bread cubes, mixed baby greens, tomato-basil cheddar and mixed heirloom tomatoes. Drizzle with dressing and toss to combine. Let sit 5 minutes to soften; serve.