Cut oysters in half; set aside. Melt butter in Dutch oven or large saucepan over medium heat. Add bell pepper and onions; cook and stir until tender. Stir in flour, salt and pepper. Cook 1 minute, stirring constantly.
Gradually stir in half-and-half, milk and reserved oyster liquid. Add potatoes and hot pepper sauce; mix well. Cook over medium heat until stew is slightly thickened and potatoes are tender, stirring frequently.
Stir in oysters and spinach. Cook until thoroughly heated, stirring frequently.