Cut tuna into one-inch squares and put them on the skewers; put in fridge.
In a medium-sized pan, saute the sliced onions and bell peppers al dente; set aside.
In a small saucepan, saute the diced onion until clear, then add chicken broth.
When it comes to a boil, add the peanut butter and crushed chili; whisk smooth.
When it comes to another boil, add lemon and pepper; simmer 2 minutes.
To cook the tuna: char rare over an open flame, saute, or broil - whichever way you choose, just don't overcook it.
Notes
To serve, lay the cooked tuna on a bed of rice or bulgur wheat, pour the sauce over the tuna, then sprinkle with bell pepper and chopped peanuts, finishing with parsley.