Brown hamburger and onion. Add refried beans, chilli powder, and oregano. Heat through (this will make the beans more liquid). Remove from heat and set aside.
In a blender combine kidney beans and pimento. Blend well. Add water. Blend again. Set aside.
Stuff the manicotti with the meat mixture and place in a greased 13x9x2 inch baking dish.
Pour the blender mixture over the stuffed manicotti.
Cover and bake at 350 °F for one hour.
Uncover, and spoon sour cream over the top. Sprinkle cheese on top. Sprinkle olives on top.
Bake 5-10 minutes longer until cheese is melted.
For an Italian flavor, omit the chili powder and add 1 Tbsp Italian seasonings.