Cook the Bacon: In a large skillet, cook the bacon over medium heat until crispy. Remove the bacon and place it on a paper towel-lined plate to drain.
Toast the Bread: Preheat the oven to 375°F (190°C). Toss the bread cubes with 1 tablespoon of olive oil, salt, and black pepper. Spread the bread cubes evenly on a baking sheet and bake for 10-12 minutes, or until golden brown and crispy.
Prepare the Salad Base: In a large bowl, combine the chopped romaine, iceberg, fresh basil leaves, and tomatoes.
Make the Dressing: In a small bowl, whisk together the lemon juice, lemon zest, Dijon mustard, whole grain mustard, mayonnaise, crème fraîche (or sour cream), agave nectar (or honey), and sriracha. Season with salt and black pepper. Slowly whisk in the reserved bacon fat and extra-virgin olive oil until the dressing is smooth and emulsified. Stir in the finely chopped basil.
Assemble the Salad: Add the toasted bread cubes and crispy bacon (crumbled into bite-sized pieces) to the salad bowl with the lettuce and tomatoes. Drizzle the salad with the prepared lemon dressing and toss everything gently to coat evenly.
Serve: Transfer the salad to individual bowls or a serving platter. Serve immediately to enjoy the crisp textures and vibrant flavors of this BLT Panzanella.