Heat 2 tablespoons oil in a 4 to 5 litre ovenproof pot over medium heat. Pat meat dry with paper towels. Add to hot oil along with onion. Brown meat on all sides. Stir onion occasionally. Add water mixed with half cup peanut butter, tomato paste and seasonings. Cover tightly and bake for 2.5 to 3 hours in a preheated 325 oven, until meat is fork tender. Lift meat to a cutting board. Cover loosely with foil and let stand 10 to 15 minutes. Skim fat from sauce. If you like, thicken the sauce by stirring in 3 tablespoons flour mixed with quarter cup water. Slice meat across the grain and serve with the sauce.