On a preheated grill roast your poblanos for about 10 minutes or until the skins begin to blister and char. Place into a bowl and cover with plastic wrap for about 5 minutes. In a medium skillet add the butter and saute the onion and red bell pepper until soft for about 5 minutes. Once cooked place into a medium bowl. In the same cleaned skillet toast the pepita seeds for about 3 minutes. Place into bowl with onions, peppers, diced tomato, cooked rice, salt, pepper and cilantro. Mix well. Carefully remove skins from poblanos. With a paring knife or your fingernail (the poblano with be tender), make a slit in the poblano from bottom to top. Pull and discard the seeds and inner membranes, being careful not to tear the rest of the poblano. With a spoon stuff poblanos with rice mixture. Top with cheese. Cover a section of the grill with foil and place the poblanos back on the grill for about 5 to 10 minutes until cheese melts. Top with a dollop of sour cream.
Boil 2 cups salted water. Add rice, cover and lower heat. Cook for about 15 minutes. Fluff with fork when done.