Preheat oven to 300.
To make the crostinis, place the sliced Ciabatta on a baking pan lined with parchment paper. Bake until crispy, about 15-20 minutes. Allow to cool completely at room temperature. If you are doing this ahead of time, store at room temperature in an airtight container for 2-3 days.
Heat the oil in a 10” skillet over medium heat. Add the onion, fennel, salt and pepper and cook, stirring frequently, until onions are soft and translucent, about 6-8 minutes. Set aside and let cool completely at room temperature.
Stack the sage leaves, roll them tight, and slice thin with a sharp knife (chiffonade).
In a mixing bowl, combine the rinsed Navy beans and cooled onion mixture. Divide amongst the Ciabatta crostinis, about 2-3 tablespoon per crostini. Top each with the sage chiffonade and drizzle with more extra virgin olive oil as desired. Serve at room temperature.