Stir the warm water, active dry yeast, and sugar together and let stand for 5 to 10 minutes, until foamy.
Mix the flour and salt in a large bowl, add the yeast mixture and olive oil, and stir until a shaggy dough forms.
Knead the dough on a lightly floured surface for 6 to 8 minutes, until smooth and elastic.
Place the dough in a lightly oiled bowl, cover, and let rise for about 45 minutes, until doubled.
Heat the oven to 450°F and line two baking sheets with parchment paper.
Divide the dough into 8 equal pieces and press or roll each piece into a 4-inch round.
Arrange the rounds on the baking sheets, spread each with pizza sauce, and top evenly with mozzarella and the optional bell peppers if using.
Bake for 10 to 12 minutes, until the crust edges are golden and the cheese is bubbling.
Cool for 5 minutes before serving.