In a large bowl, dissolve the yeast in 1/2-cup warm (110F) water. Allow the yeast to proof until it is foamy, about 10 minutes.
Add the remaining 1 cup warm water, combining it well with the yeast. Add 3 cups of the flour and the salt. Mix the dough with your hands or use a mixer with a dough hook, adding the remaining flour as needed to make dough that holds together.
Place the dough on a floured surface and knead it for about 10 minutes, or until the dough is soft and not sticky. Grease a bowl with the olive oil. Put the dough in the bowl and turn a few times to coat with the oil. Cover the bowl tightly with plastic wrap and let it rise for 2 hours in a warm place.
Preheat the oven to 375 F.
Punch down the dough and knead it for a few minutes on a lightly floured surface.
Divide the dough in half and roll each out on a floured surface into a 12-inch diameter and place the rounds on lightly oiled 13-inch pizza pans. Turn in the edges of the dough about 1/2 inch to form a rim. You can stretch the dough to fit an even larger pan if you wish.
Blind bake the pizzas until they puff up and are golden brown. Transfer them to a cooling rack and when warm, spread the Nutella over the top of each one and arrange the banana slices on top of the Nutella.
Cut into wedges to serve.
Another option is to make personal size pizza by dividing the dough into 8 equal pieces and stretching each one into a 6-inch diameter.