Heat oil over medium-high. Add bacon, and cook, stirring often, until golden brown and almost crisp, about 3 minutes. Add scallion whites and cook, stirring, until softened, about 1 minute. Add pinto beans and water, and season with salt and pepper. Bring to a boil; reduce heat and simmer, stirring occasionally, until slightly thickened, about 5 minutes. Serve topped with scallion greens.