For the Flatbread Croutons:
Place flatbread on cutting board or work surface and, using a sharp knife or pizza wheel, cut it into 1/2-inch squares.
Preheat a large nonstick skillet over medium-low heat. Spread the flatbread squares out evenly in the preheated skillet. Toast the flatbread squares until they're a little golden-brown, crispy, and fragrant, about 5-7 minutes, stirring occasionally.
Remove toasted flatbread squares from skillet and allow to cool completely (they'll become crispier as they cool). Set aside (or to make these ahead, once cooled, store in a zipper bag until serving).
For the Honey-Balsamic Vinaigrette:
In a small bowl, whisk vinegar, oil, honey, salt, and pepper until combined. Set aside (or to make this ahead, cover and refrigerate until dressing the salad, re-whisking again as needed).
For the Kale Salad:
In a large bowl, combine kale, cannellini beans, cherry tomatoes, sun-dried tomatoes, basil, feta, parmesan, red onion, and red peppers. Toss thoroughly but gently.
Add the dressing and toss again to distribute the dressing evenly.
If serving the salad immediately, sprinkle flatbread croutons on top. However, the salad can be refrigerated for up to a day (the kale will continue to soften if you've already added the dressing) – wait to sprinkle the croutons on top until just before serving so they stay crispy.
Parmesan and Feta Cheeses: To make this kale salad recipe truly vegetarian, be sure to select a parmesan cheese made with non-traditional enzyme alternatives from microbes or fermentation, rather than the traditional rennet. In addition, be sure that your feta, which is often made with vegetable rennet, specifically lists that as an ingredient, rather than just listing "rennet," which may be animal-produced.
Kale: As noted in the post, I usually grab pre-chopped, bagged curly green kale. Even though a lot of the larger parts of the tough stems have been removed from the bagged, pre-chopped kale and the leaves are somewhat chopped, for this salad, I still remove any remaining sections of stem and further chop the kale into confetti bits. Refer to the photos in the post as examples. Also, to make this an even more "Tuscan" salad, you can substitute Tuscan kale if it's available.
Make-Ahead Tips: This salad can be served immediately, or refrigerated for a few hours, up to a day ahead. In addition, most of the salad's components can be prepped even further in advance. As noted above, you can make the flatbread croutons ahead of time and, once cooled, store them in a zipper bag until serving. You can also make the vinaigrette ahead, then cover it and refrigerate until needed (you will probably need to re-whisk it again before adding it to the salad). Lastly, most all of the salad ingredients and veggies can be chopped a day or two in advance of assembling the salad. (In general, however, I recommend not chopping the basil until assembling your salad, so it's fresher.)