Preheat oven to 425 degrees F (220 degrees C). Grease a 1 1/2 or 2 quart casserole dish.
In a small bowl, combine baking mix with 2/3 cup milk and knead until the dough pulls together. Turn the dough onto a floured surface and form into a rectangle 1/4 to 1/2 inches thick. Arrange 1/2 of the pimento cheese and the pimentos on the dough and roll up the dough lengthwise.
Cut the roll into 6 equal portions.
In a large saucepan, cook onions and bell pepper in butter until soft.
Pour soup into the saucepan, along with 1 cup milk, tuna, and 1/2 of the pimento cheese. Cook the mixture over a medium heat until the cheese is melted.
Pour the mixture into the prepared casserole dish. Arrange the 6 slices of dough, cut-side down, on top of the sauce in the casserole dish. Push the dough into the sauce.
Bake in preheated oven for 25 minutes or until whirls are golden brown.