Heat 2 tablespoons oil in a 4 to 5 qt. 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 1/2 cup peanut butter, tomato paste and seasonings. Cover tightly and bake for 2 1/2 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 1/4 cup water. Slice meat across the grain and serve with the sauce.