Preheat a grill pan over high heat.
Bring 2 cups vegetable broth and butter to a boil in a small covered pot. Add rice, reduce heat to low and cook 18 to 20 minutes, or until rice is tender and liquid is absorbed.
Split peppers lengthwise and remove seeds, leaving stems in tact. Grill peppers on hot grill pan for 3 to 5 minutes on each side. Remove from grill and let cool enough to handle.
To a medium skillet over moderate heat, add 1 tablespoon oil and onion. Saute onion 2 or 3 minutes. Add cooked rice to the pan and stir in peas and taco sauce. Season rice with salt and pepper.
Load up pepper halves with seasoned rice. Top rice filled peppers with chopped cilantro or parsley and scallions.