Missing wall insulation

Hi all, I’m in a house built 7 yrs ago. One bedroom wall faces East and gets strong morning sun. It’s a gyprock wall with hebel exterior. One section of the wall, about 600x300 gets very hot in the mornings on sunny days. I’m thinking that some insulation is missing. Is injectable spray insulation the quick remedy? There’s no power or lighting in the area. Cheers