Cook onion, celery, green pepper in butter until soft. Blend in flour, salt, pepper and garlic powder. Add chicken broth, peas, corn and cook over medium heat, stirring constantly, unti mixture is thickened and bubbly. Combine onion mixture with chicken and pour into a greased 2 qt casserole. Put in a hot oven 425 to heat while you make the biscuits. Prepare biscuits mix, using 2/3 cup milk as directed on package. Turn onto a lightly floured surface and knead a few time. Roll out to an 8" square; sprinkle with the cheese. Roll as for jelly roll, sealing the edges. Cut 8 slices 1" thick. Place on the hot chicken mixture in casserole and sprinkle with paprika and bake until the biscuits are lightly browned, about 25 minutes.