\documentclass{report}
\usepackage[explicit]{titlesec}
\usepackage{tikzpagenodes,showframe}
\titleformat{\chapter}[display]
{\normalfont\huge\sffamily}
{}
{20pt}
{%
\begin{tikzpicture}[remember picture,overlay]
\node[
anchor = west,
rectangle,
minimum height = 4cm,
text width = \paperwidth,
xshift = -\the\dimexpr\oddsidemargin + 1in + 1cm\relax,
outer sep = 0pt,
fill = red!50] (titlerect) {};
\node[
anchor = south west,
xshift = 3cm,
text width = \textwidth]