Heat oil in large skillet on medium-high heat. Add bell pepper and onion; cook and stir 4 to 5 minutes or until tender. Stir in tomatoes, water and Seasoning Mix. Bring to boil. Reduce heat to low; simmer 5 minutes. Add chicken, rice and beans; cook and stir until heated through.Spoon about 1/2 cup chicken mixture onto each tostada. Serve with assorted toppings such as cheese and sour cream, if desired.Want to make your own Tostadas? Preheat oven to 425°F. Lightly spray both sides of 16 (6-inch) tortillas with no stick cooking spray. Press each tortilla into a small oven-safe bowl to form a cup shape. Place bowl(s) on baking sheet. Bake 8 minutes or until edges are browned. Let cool 3 minutes. Remove tortillas from bowls; cool completely. (Prepare tortilla bowls in batches.)